 I welcome you all for the module 6 lecture 2. In this lecture we will be covering the following topics, the measurement of pitch, wherein we will be discussing the use of pitch measuring machine and use of tool makers microscope, screw pitch gauge and profile the projector and then we will move to measurement of effective diameter, wherein we will be discussing about 2 wire method, 3 wire method and use of thread micrometer. Now, we will start the measurement of screw thread pitch. The most commonly used methods for measuring the pitch are pitch measurement using pitch measuring machine, use of tool makers microscope, use of screw pitch gauge and then use of profile projector. Now, this diagram shows the pitch measuring machine. So, we have the base made of cast iron very sturdy base and then we have centers, 2 centers are provided for mounting the screw thread and then there is a carriage which will move parallel to the axis and then in the carriage there is a stylus mounted on spring loaded head and then we have 2 indicators, one is a fideosial indicator to ensure that same pressure is maintained throughout the pitch measuring and then there is another indicator K to indicate that stylus is in the proper location and then we have a micrometer using this micrometer, when we rotate the micrometer the head measuring head will move. So, because of when the measuring head moves parallel to the axis the stylus will move in against the spring the pressure and then when the carriage further moves it will move down into the groove and its get seated in the next groove. The distance moved from the first position to the next position will give us the pitch of the screw thread. A set of stylus is supplied along with the machine, along with the selection guidelines. So, depending upon the type of thread and pitch of thread etcetera, we have to select the appropriate stylus and then we have to mount the stylus in the head. So, accurate positioning of the stylus between the 2 flanks is obtained by ensuring that pointer K is always opposite its index mark when readings are taken. That means when the stylus is in the proper position when the stylus is placed like this between the flanks, the pointer K will indicate whether the pointer K should be just against the reference mark. So, this is the pointer K the stylus of the pointer should be against its reference. So, this indicates that the location of the stylus in the thread groove is proper and pointer T that is a fiduciary indicator ensures uniform pressure. The difference between the 2 readings that means the stylus is placed in the first thread groove and the micrometer is reading is taken and then it is moved to the next groove. So, the distance moved by the stylus from the first position to the next position gives the pitch. Now, this pitch measurement can be carried out for 5, 6 or more than for all the thread grooves and then average pitch value can be calculated. Now, this picture shows the arrangement of pitch measurement. You can see we have a center on which the screw thread is mounted and we have a bar which carries the stylus. The stylus will move from one thread to the next thread and it gets seated into the in the thread groove and then the micrometer is reading is taken and then it is moved to the next thread. So, like this we can measure the pitch and the stylus always contacts the flank approximately at the pitch line. Now, internal thread measuring machine and how do we check the pitch of internal thread? You can see here the arrangement is we have a bar which carries the ball ended stylus and there is an arrangement to mount the workpiece with the internal thread. The bar along with the stylus will move in and it gets seated into the thread like this. So, we will be having the screw thread like this. So, this bar with the stylus will move into the workpiece having the screw thread. So, this is the bar and this is the stylus the ball end stylus and this is the pitch line. Now, this ball end will be seated in the groove approximately at the pitch line and then the micrometer reading is taken and then it is withdrawn bar is withdrawn and then it goes to the next position again it gets seated ball is will be seated like this and again other reading is taken. So, the difference in reading gives the pitch of internal thread. Now, tool makers microscope can also be used for the measurement of pitch. The construction of the tool makers microscope is shown in this schematic diagram. We have a sturdy cast iron base and there is a column. The work table work table is mounted on the base. The work table can be moved in x and y direction that is it can be moved perpendicular to the column like this and it can be moved parallel to the column. So, for moving the table you can see the micrometer screws are provided and then the table carries a glass plate. The workpiece should be placed on the glass plate and the light will move pass through the workpiece and the shadow image will be obtained on the screen which can be observed through the eyepiece. So, this is the eyepiece through which we can observe the shadow and then this is the optical head which carries all the collimating lenses and then eyepiece and this is the objective. The magnifications can be selected depending upon the requirement like the objective may be some 3x magnification or 10x magnification. Similarly, eyepiece magnification can be selected. This optical head can be moved up and down for focusing purpose. We can see there are guideways are provided for movement of optical head and there is a wheel which can be used to move the head up and down and it can be clamped. This is the clamping screw after focusing the head is clamped and this is the wheel for moving the head up and down and this is the optical system of microscope. You can see the body has a lamp normally tungsten filament lamp is used and there are set of lenses collimating lenses to get parallel beam of light and there is a mirror. So, using which the light beam is diverted and we have a glass plate here over which we can place the workpiece. So, workpiece should be placed here for example, we want to measure the pitch the screw thread is placed on the glass plate. Light will pass through the workpiece and we get the image which we can observe through the eyepiece. Now, these tool makers microscope they have a movable and rotatable tables. The table can be moved in the x and y direction. So, that we can take the measurement and it can be rotated also. So, this will be very useful while measuring the thread angle of the workpiece. The optical head can be moved up and down for focusing purpose and there is a glass plate on work table to mount the workpiece. So, that the light will pass through the glass plate and it will pass through the workpiece and we get the shadow image. Light sources are provided which will give us horizontal beam of light which is deflected by mirror by 90 degrees upwards through the table. A surface elimination is also possible whenever we want to measure the surface characteristic of workpieces, this surface elimination can be used. The image that is the contour of the workpiece is projected in the ground glass screen which has the scale also rotary scale as well as it has cross hairs using which we can take the measurement. The measurements are made by moving the cross lines engraved on the ground glass screen. The magnification can be selected depending upon the size of the workpiece. If it is very small then higher magnification can be used and similarly light intensity can also be selected. So, now we shall see a tool makers microscope and we will understand the construction and how it works. I can see the tool makers microscope, the construction I can see this is the work table. This can be rotated also I can see the grooves are provided for fixing the fixtures workpiece fixtures and then the table can be moved parallel to the column this is the column of tool makers microscope. Table can be moved parallel to the column and perpendicular to the column using these micrometer wheels. These micrometers they have a very fine accuracy the least count of this these micrometers is one micron. We can see the column and you can see the rack also and we have a wheel here for moving the optical head up and down for focusing purpose and we can see the eyepiece and then this is the objective. The lenses of objective and eyepieces can be changed to get the required magnification and below this table we have a light source through which we get the beam of light. For surface elimination purpose we have another light source placed in the measuring head. This is the eyepiece and you can see the objective now it is 3x objective is placed. You can also see the rack which is used for up and down moment of the head. These are the micrometers for moment of table in x and y direction that is parallel to column and perpendicular to column. You can see the glass plate on which the workpiece can be mounted. Here we can see the main switch and then two black rotary knobs are there. So, this one is used to get the surface elimination. You can see the light source light is reflected back. So, this surface elimination is used whenever we want to check the surface characteristic and this knob we have to use when we want to get the shadow images of shadow contours of the workpieces. The least count of this micrometer is 0.001 millimeter main switch surface elimination knob. You can see the brightness can be adjusted. This is half position brightness 1, 2, 3, 3 brightness different intensities we can have. So, similarly this is for vertical elimination to get to get the contours of the workpieces. Again brightness can be adjusted through elimination. So, using this tool makers microscope we can measure the various thread elements like pitch of the screw thread and then thread angle and then major diameter, minor diameter. So, all thread elements can be accurately measured. So, whenever the workpieces, screws are very very small, we can get the magnified image and then the measurements can be obtained. So, whenever it is not possible to use other types of instruments like thread micrometer or outside micrometer, then this tool makers microscope will be very useful. Now, we will move on to the use of screw pitch gauge which is used to measure the pitch of screw thread. Now, in this picture shows a set of leaves you can see here arranged in a handle and the what is the pitch value is marked on each leaf. So, by trial and error we can measure the pitch of the screw thread and a light source is needed to check the pitch. That means we have to say this is the screw thread, this is the workpiece having the screw thread, we have to select a leaf which will match with the this is the gauge pitch gauge and backside we should have a light source. So, we get the light and then we should observe in this direction. If the light passes between the pitch gauge and workpiece, then the match is not perfect then we should change the gauge and this process we should continue till the light will not pass through the gap between pitch gauge and workpiece. Like this we can measure the screw pitch gauge, we can measure the pitch using the screw pitch gauge. Now, let us see how we can use a pitch gauge to measure the pitch. So, we have a screw thread whose pitch is to be measured, it is held in left hand and pitch gauge is held in the right hand. We should select the pitch gauge, a particular leaf should be selected and it is placed on the screw thread. If the match is pukka which so this combination should be viewed against a light source, if the light does not pass between the gap then the match is pukka and we can read the pitch value that is mentioned on the leaf. Now, we can see 1.75 is mentioned on this leaf. So, the pitch of this screw thread is 1.75 millimetre. Now, profile projector is also used to check the pitch of the screw threads. The working principle is similar to the working principle of tool makers microscope. In the profile projector the image of the workpiece that is screw thread is obtained on the ground glass screen and then by moving the image against the reference cross lines we can measure the thread elements like pitch, thread angle etc. Those elements can be measured. So, very delicate and small screw threads can be easily measured using profile projector and thread profile is amplified and parameters are measured by movement and comparison methods. Chord gauges are used for comparison purpose. So, depending upon the type of screw thread whether it is a Witwer thread or metric thread or Akme thread we should select appropriate chart gauges and the chart gauge should be mounted on the viewing screen. So, this is the chart gauge. So, which will have two contour lines and then we should obtain the image of the contour of the workpiece. If the image lays between the two lines on the chart gauge then this is the image obtained. So, if it lays between these two lines this is corresponding to the maximum size and this is corresponding to the minimum size. So, this is the tolerance band. If the image contour is well within the tolerance band then workpiece is accepted. So, this is the comparison method. In the movement method on the screen we observe two cross lines. So, if we want to measure the pitch of the screw thread we should get the image and then we should move this cross line. So, that it means the crust here and the micrometer reading is taken then it is moved to the next position. Again it is in at this particular place that is crust of the next thread and then again the micrometer reading is taken. So, the difference between these two micrometer readings gives the pitch of the screw thread. So, this is how we can use the profile projector for pitch measurement. Now, let us see a profile projector to understand how the construction and working of a profile projector. Now, you can see the viewing screen of profile projector and we can also see the image of the screw thread the contour of the screw thread. We can observe the vertical cross line and horizontal cross line. Now, the horizontal cross line is contacting the crust of the screw thread. Now, it is in contact with crust of screw thread. I can see the protractor ring with the vernier. I can see the display x and y display both are reading 0. Now, the cross line is moved. So, when we operate the micrometers the stage will move and the image will also move. Now, we can see the cross here is touching the crust on the other side and now we can see the reading. So, the stage has moved towards the column and initial reading was 0 and now it is reading 11.657. So, 11.657 millimeter is the major diameter of the screw thread. Now, again we are moving the work table. You can see the cross line is moving and now both x and y are 0. Now, again we are moving the image. Now, you can see y is showing minus 9.672. So, this is the minor diameter of the screw thread. That means horizontal cross line has moved from root to root. So, which will give us the minor diameter of the screw thread. Now, I can see the cross horizontal cross line is in contact with the root. So, using profile protractor we can measure minor diameter, measure diameter, pitch, thread depth, thread angle etcetera. Now, we will move to the measurement of effective diameter. Effective diameter measurement is carried out by the following methods that is by using 2 wire method, 3 wire method and by using thread micrometer. So, this thread micrometer method is a direct method which involves no calculation. It directly measures the effective diameter, whereas the first two methods they will not give the direct effective diameter diameter. We have to calculate effective diameter. So, 2 wire method, the wires of exactly known diameters are chosen such that they contact the flanks at their straight portion. That is, say we have this screw thread. So, we have to select wires which will make contact with the flank like this. So, this is the pitch line. So, the wire will make contact and the straight portion of the flanks. If the size of the wire is such that it contacts the flanks at the pitch line, then it is called the best size of the wire which can be determined by geometry of the screw thread. So, this is the screw thread profile and this is the pitch line. If the screw thread, if the wire size is such that it contacts the flank exactly at the pitch line, then it is called best size wire. The screw thread is mounted between the centers and wires are placed in the grooves and reading M is taken. Reading M means measurement over roller. So, then after finding M, the effective diameter can be calculated using this relationship E is equal to T plus P where T is equal to M minus 2 D. M is measurement over rollers which is obtained by micrometer and small D is the wire size. So, when we deduct twice wire diameter from the M, we get T and then we can calculate effective diameter using this relationship E is equal to T plus P and P is a value which depends on diameter of wire, pitch of screw thread and angle of screw thread. Now, you can see here in this schematic diagram, we have the screw thread. This is the screw thread gauge is the workpiece whose effective diameter is to be measured and we have two wires. One wires or rod is placed in the groove and in the opposite groove, we have placed another wire of known diameter small D. Small D is the diameter of this wire. Now, we can see the rod has entered into the thread and some portion of the rod is below the effective, below the pitch line. So, this is the pitch line and this is the ball lowest point. So, this gap is equal to P by 2. Similarly, on the other side we have P by 2. So, we can measure the M that is measurement over wires so this is M. So, this is M dimension over the wire. This can be measured using a micrometer. Then, effective diameter can be calculated by using this T. T is measurement under rollers measurement under rollers plus P. So, P by 2 here and P by 2 here we have to add. So, we get E is equal to T plus P where T is measurement under rollers which can be obtained. So, T is equal to M minus D minus D, M minus 2 D. So, T can be obtained. M is obtained by measurement diameter is known. So, T can be calculated and P it depends on the thread angle pitch which can be calculated. I can see two wires or two rods are placed. This is the workpiece having a screw thread. Two rods are placed in the opposite direction and these are the animals of the micrometer. So, this shows the measurement of M measurement over roller and this will indicate micrometer, will indicate what is the value of M. So, these two rods we can hold them by hand or we can use a machine known as floating carriage micrometer which we will discuss after some time. So, some arrangement is provided, hooks are provided in the floating carriage micrometer. So, the rods can be hung from this hook. Now, T is the dimension under wires which is equal to M minus 2 D and M is dimension over wires. D is diameter of each wire, P dash is pitch of the thread. Then we can calculate P. So, in the previous picture we discussed about this P which depends upon thread angle and pitch. It can be calculated using this relationship for metric thread capital P is equal to 0.8 double 6 P dash minus D where D is the diameter of rod and P dash is the pitch thread. So, this P value we can insert here and T can be calculated then E can be calculated. So, this shows the geometry of two wire method. So, we have this groove and then this is the wire of diameter D and we have to measure the diameter M by using outside micrometer and this is diameter T below the under the wires and this is the pitch line and this is the effective diameter and x is the flank x is the thread angle x by 2 is the flank angle. Now, by following this derivation we can get the value of P which depends upon the wire diameter and the flank angle. So, once we get the P we can also get T, T is equal to M minus 2D. So, by knowing T and P we can get the value of E effective diameter. Now, we will move to the another method 3 wire method. This is the more accurate method. The reason is in the case of two wire method. So, we have this thread like this. So, we have one rod here and another rod here and then these are the animals of the micrometer. So, these two rods they are not in the plane perpendicular to the axis. There is some inclination. So, because of this the animal faces while measuring the animal faces may slightly deflect they will not be parallel. So, because of that some error will be introduced in the case of two wire method. In case of three wire method there is the faces animal faces are parallel to the thread axis. Since we are using three wires and on the other side we have two wires one wire here and another wire here. In the case of three wires. So, this is the thread profile. So, we will be placing one wire here and we will be placing two wires on the other side and then we have the anvil. So, because of this arrangement the chances of deflecting the animal surface animal face is very less and these two faces animal faces will be parallel and the measurement error will be less. Hence, this three wire method is more accurate. So, in this method the three wires of equal and precise diameter are placed in the grooves as shown here. The wires may be held in the hand or we can hung from a hook which are this arrangement is available in the floating carriage micrometer. So, you can see the schematic diagram we have placed one wire here and two wires here and p is the pitch of screw thread d is wire diameter and this is the measurement over wire. You can see the arrangement here where two three rods are there the workpiece that is screw thread is held between anvil and two rods are placed here and one rod on the opposite side. So, it will be very difficult to handle the workpiece micrometer and three rods together. So, it becomes time consuming. So, for easy handling cylinders can be obtained in sets which are mounted in cages. So, using these cages it will be easy to measure the effective diameter by three wire method. Now, this shows a floating carriage micrometer. You can see the cast iron base and then we have two centers. Two centers are provided for mounting the workpiece. The centers can be moved in and out to accommodate the workpiece of different sizes and the centers can be clamped by operating these levers. Now, perpendicular to the center axis we have another axis wherein a micrometer with large diameter thimble is provided and on the other side we have a fidizial indicator to indicate the measurement pressure. So, the workpiece is mounted between the centers and measurement can be taken using this micrometer and for all measurements we can always apply the proper pressure or the same pressure. You can see here the arrangement is provided. The hooks will be provided here so that the prisms or the rods can be hung from the hooks. So, this will help in the measurement of minor diameter and in the effective diameter. So, this carriage which is carrying the micrometer moves on ball tracks freely. Hence, it is called floating carriage micrometer. For measurement of minor diameter reading is taken using suspended prisms. Prisms can be suspended here and the readings can be taken. For measurement of effective diameter reading is taken on suspended cylinders or suspended wires. I can see the hook here. This is the hook to mount the cylinder or prism. You can see the rod cylinder is hung from this hook. We have one rod here, we have another rod here. This is the workpiece screw thread and these two are the centers. The workpiece that is screw thread is mounted between the centers and then we have the measuring anvils. So, I can see there is a digital indicator. So, directly it shows maybe the measure diameter, minor diameter and minor diameter and effective that is measurement over roller. So, such things it will directly indicate and here you can see again rods are there by which we can place the prisms or rods conveniently. So, these centers can be moved in and out to accommodate the workpieces of different size. This body can be moved and it can be clamped at any desired location. Now, in the commercially the floating carriage micrometers are available with specifications like this. Base is made of cast iron material. Maximum longitudinal measurement is 90 mm. Different longitudinal movement is possible 100, 120 like that they are available. Maximum traverse measurement is 30 mm on each side. Least count of zero indicator is 0.01 mm and least count for micrometer is 0.001 mm. Micrometer range is 0 to 25 mm and a master piece is provided with the machine whose diameter is 16 mm. If we require a master piece of different diameters which they are available in the market, specimen size m 16 times 2. One specimen is provided with the machine for wire size is 1.35 mm for 3 wire method. If you want a set of wires that is also possible overall size of the machine is 300 by 300 times 200 mm and weight will be normally 10 kg. Now, the geometry of 3 wire method on one side we have placed 1 cylinder or wire on the other side we have 3 2 cylinders. So, this is the pitch line and this is the effective diameter and m is measurement over rollers and roller is placed in the groove. Now, you can see the roller is not contacting the flank at the pitch line that means this is not a best size wire. If it is best size wire then the wire will contact the flank at the pitch line like this at the pitch line the wire will contact. I can see here this is the pitch line and the wire is contacting the flank at the pitch lines. Then this wire is called best size wire and we have the thread angle. So, m is measurement over roller and p is pitch small d is the diameter of wire and this is flank angle. So, h is the center rod or cylinder center height from the pitch line that is h and capital H is thread depth. So, from the previous figure m is capital M is diameter over wires, e is effective diameter which is to be determined, small d is the diameter of wire, h is height of wire center above the pitch line or is radius of wire, capital H is depth of thread and d is capital D is major diameter of the thread. Now, using the geometry we can derive the relationship between effective diameter and the measurement over roller the derivation is presented here. m is measurement over roller and e is effective diameter, d is the diameter of wire, theta is the thread angle and p is pitch. So, by measuring m and by knowing d and theta and by measuring p we can get the effective diameter. For metric threads, for metric depth of thread that is capital H is equal to 0.6495 p and then effective diameter is equal to d this is the major diameter of the screw thread d minus 0.6495 p. So, we can measure the value of m practically using the micrometer or floating carriage micrometer and then we can calculate e. Now, you can see this is the geometry which shows the best size wire placed in the thread groove. You can see the contact the wire is contacting the flank at the pitch line. So, if this is the case then such a wire is called best size wire. So, wherever possible we should calculate the best size wire and then the nearest wire, nearest size the wire should be selected and then it should be used for measuring the effective diameter. I can see here. So, db is the diameter of best size wire this is equal to p by 2 secant theta by 2 where p is pitch and theta is thread angle. So, theta will be 60 degree for metric screw thread and pitch can be measured using pitch gauge and then db that is best size wire can be calculated and then we have to see what is available the set of wires we have to see and we should select a wire which is almost equal to the best size wire that is calculated. For a metric thread the acceptable range of wires is shown here the maximum wire diameter can be up to 1.01 times p where p is pitch and the best size wire is equal to 0.577 p and then minimum wire diameter is 0.505 p. So, we can select the wire within this range and then we can use them to find the effective diameter of the screw thread. Now, we will conduct an experiment to show how three wire method can be used for measurement of effective diameter. You can see the standard wires of different diameters. The diameters is measured and it is mentioned you can see this is the cage which carries three wires of same diameter. This is the single cage with single wire of 1.65 millimeter and in this cage we have two rods or two wires with the same diameter 1.65 millimeter. So, like this complete set is available with different diameters. So, we should calculate what is the best size wire depending upon the type of thread that is pitch and thread angle and then nearest wire that is available in this set should be taken out. You can see 1.35 millimeter diameter. This is the screw thread whose effective diameter is to be measured micrometer. So, we have checked the pitch of the screw thread and we found that it is 2.5 millimeter and then the best size wire is calculated using the relationship p by 2 secant theta by 2. So, theta since we have selected the metric thread theta that is thread angle is 60 degrees and pitch of the given screw thread is 2.5 millimeter. So, best size wire is 1.4434 millimeter. Now, we are selecting a best wire of 1 wire. We are selecting a wire of 1.35 millimeter and this is the screw thread. You can see how to hold the wires. So, we have a hole in the cage. So, the cage can be inserted into the anemones. So, now the two cages they are placed in the opposite side. One wire is on one side and two wires on the other side of the screw thread and then slowly we have to rotate the thimble of the micrometer. So, that the anvil advances the spindle advances. Now, we can take the measurement over roller that is m. Now, we can take the reading measurement over roller is 15, 16, 17, 18, 19, 20, 20 millimeter and then 0.05, 0.09, 20.09 millimeter is the m. We can also see the third decimal place. So, the main scale reading is 20, thimble reading is 0.09 and then third line is coinciding with this line. So, m is 20.093 millimeter. So, now we know the m and we know the diameter of rod used. We know the thread angle 60 degree pitch is 2.5 millimeter. Using these values, we can calculate effective diameter E. I can see the close view of the arrangement, close view of the arrangement. We have a single rod here and two rods this side and this is the workpiece having the screw thread and the micrometer. So, now we can see the reading. It is main scale reading is 20, 20.093 millimeter. Now, we will solve some numerical problems. The first problem we have to calculate the diameter of best size wire for an m20 times 2 screw thread. The data that is given is pitch of the thread is equal to P is equal to 2 millimeter and since it is metric thread, the thread angle theta is 60 degrees. Now, using this relationship 0.5 double 7 P, we can calculate the best size wire diameter. That is 0.577 times 2 is equal to 1.154 millimeter is the diameter of the best size wire. Now, we will move to the second problem. We are required to calculate the best size wire diameter and the difference between size under wire and effective diameter for a m16 times 2.5 external screw thread. Data that is given is pitch is equal to 2.5 millimeter. So, we can calculate the best size wire is equal to D is equal to 0.577 times P that is equal to 1.442 millimeter. Then from this picture, I can understand that we are required to calculate the difference between size under wire. So, this T is the size under wire and effective this is effective diameter. So, E minus T this is equal to P by 2 here and P by 2 here. So, when we add this to it becomes P. So, E minus T we have to find. So, capital P is equal to 0.866 times P minus D. So, this is equal to 0.723 millimeter. So, difference between size under wire and effective diameter is 0.723 millimeter. In the third problem, when measuring the effective diameter of an external screw thread of 3.5 mm pitch, a 30 millimeter diameter cylindrical standard and 2 millimeter wires were used. The micrometer readings over the standard and wires and over the screw thread and wires were 13.376 and 12.242 millimeter respectively. We are required to calculate the effective diameter of the screw thread. So, the data that is given is R1 is equal to reading over standard reading over standard and wires is 13.376 millimeter and R2 is reading over screw thread and wires is 12.242 millimeter and the standard cylinder diameter is 30 millimeter and diameter of wire is 2 millimeter. Pitch of the screw thread is 3.5 millimeter. So, we can calculate the T size under wire is equal to S minus R1 minus R2. So, the diameter of the standard is larger. So, like that we have taken. So, T is equal to S is 30 millimeter and R1 minus R2 the values should be inserted. So, finally we get T is equal to 28.866 millimeter. Then P is equal to 0.866 times P minus D. So, P will be equal to 1.031 millimeter. Then effective diameter is equal to T plus P. So, that is 28.866 plus 1.031 millimeter. This is equal to 29.897 millimeter is the effective diameter. Now, we will move to thread micrometer. Using the thread micrometer we can measure the effective diameter directly. This picture shows a thread micrometer. I can see the here we have a hollow anvil and again this side we have hollow spindle. So, in the hole on the spindle as well as anvil we can insert these replaceable anvils. So, depending upon the pitch of the screw thread we can select appropriate anvils and we can insert them and we can get the effective diameter directly by using this thread micrometer. You can see the close view or this is the spindle with a pointed end and this is this anvil is placed in the other side. So, now the thread micrometer will directly give the pitch diameter. You can see the tips are not sharp they are made flat. So, if they are very sharp chances that the point may touch the root. So, to avoid that the tips are made flat and similarly here again the tips are made flat. So, that they will not contact the root they will contact only the flank. A set of anvils will be available. So, depending upon the pitch of the screw thread and the type of screw thread whether it is metric or bitware we have to select appropriate anvil. So, if the pitch is 1.25 millimeter then we have to use this set. If it is bit worth thread with 12 tpi then we have to select this set. So, like this depending upon the type of screw thread we have to select appropriate anvils and we have to place them in the screw thread micrometer and then we can directly measure the effective diameter. Now, let us conduct an experiment to measure the effective diameter of a screw thread using thread micrometer. You can see this is the screw thread micrometer range is 0 to 25 millimeter and least count is 0.01 millimeter. You can see the anvil can be moved in and out to accommodate the workpiece of different lengths. The range of this instrument is 0 to 25 millimeter and the least count is 0.01 millimeter. Now, this is the set of anvils depending upon the type of screw thread we have to select appropriate set appropriate pair should be selected and should be used. Now, I am selecting m 1.75 I am using a matrix screw thread with 1.75 pitch. So, I selected this particular pair you can see the tips are made flat they are not very sharp. So, I have selected 1.75 pair we have to insert the anvils into the micrometer and then we should advance the spindle till it comes in contact with the anvil. This is essential to check with whether there is any 0 error. If 0 error is there we should move the anvil and we should make it 0 otherwise we should account for the 0 error. Now, the spindle is in contact with the anvil. Now, you can see there is a small error of 0.8 millimeter. So, 0 error is 0.8 millimeter. This should be subtracted from the reading given by the micrometer. The screw thread should be held between the anvils and slowly we should advance the spindle. The two anvils should contact the screw thread at the maximum size. Now, you can see the spindle and anvil. The anvils are contacting the flanks. Now, we can take the reading. The reading is 0.54, 10.5 plus 0.4 that is 10.9 millimeter. So, the reading given by the micrometer is 10.9 millimeter 0 error is 0.8 millimeter. So, we should subtract this from the reading given that is 10.9 minus 0.8 millimeter that is equal to 10.1 millimeter is the effective diameter of the given screw thread. Now, with this let us conclude this session. In this session we discussed about the pitch measurement and effective diameter measurement. We studied about different methods of measuring the pitch that is optical methods and use of screw pitch gauge and then we studied about the measurement of effective diameter. So, wherein we discussed about 2 wire method, 3 wire method and use of screw thread micrometer to get direct measurement of effective diameter. With this we will conclude this session. Thank you.