 I welcome you for module 3 lecture 7. In the last lecture, we started discussion on various kinds of limit gauges. We will continue the discussion. Now, we have a plane ring gauges. See, these ring gauges, they are used to check the shafts that is the external features diameter of the shaft. If the external feature that is diameter of shaft is plane, that means there are no threads, then we use these kind of plane ring gauges. Now, we can see here normally they come in a pair, one for go and other for no go limit. So, again these are made as per IS 3455 of 1971. Also, one more standard that is followed is IS 3485 of 1983. So, all these gauges, they are made to the accuracy of IT 1 grade. Now, in these standards they are mentioned what should be the size of the outer portion and what should be the thickness of these ring gauges and it is necessary that we have to mention the size, the basic size with the tolerance and then manufacturer details. All those things are to be mentioned as per these Indian standard. They are available with different materials, gauge materials. If it is carbide, they are available in this particular range 6 millimeter to 40 millimeter and in hardened steel, they are available from 6 to 100 millimeter. If the bigger size gauges, ring gauges are needed, they can be manufactured as per the customer requirement. Now, we have this carbide ring gauge in a steel ring. That means, it will be like this. So, we have this steel ring and then inside, we have carbide ring. So, this is carbide ring, outside is steel, inside is, this is only to save the material, carbide is costly compared to steel. So, the outer body is made out of steel and this gauging portion is made out of carbide. So, it becomes economical. Now, these are adjustable indicating snap gauge. So, you can see here, these are adjustable snap gauge. The reason is the distance between the measuring faces can be adjusted and then indicating. You can see here, there is an indicator with limit setter. Two limit setters are there. One can be set to lower limit and another one can be set to upper limit and then when we use these adjustable indicating snap gauge, when we insert the workpiece here, shaft here, the pointer will move and if it is between the upper limit and lower, these two limits, the workpiece is accepted. If it is below the slower limit and above the, it moves after the upper, this particular limit, then the workpiece is rejected. There are some special features in this adjustable indicating snap gauge. There is a lever. We can see here, backside of this tool, we have a lever. So, when we operate this lever in this direction, this spindle or the measuring face will move in. That means, this will move in and then we can insert the workpiece, so that it will come in contact with this anvil and the adjustable center stop and then we have to release this lever, so that this moves in the reverse direction due to spring and then it comes in contact with the workpiece and then we can see the position of the pointer. Then, we can accept or reject depending upon the position of the pointer. Now, this adjustable center stop is provided for automatic alignment of the workpiece, so that the center of the workpiece is in line with this axis. So, for that purpose, this adjustable center stop is provided. Depending upon the workpiece size, this can be adjusted and then we can adjust the range of this snap gauge by moving this anvil in and out. We can see here, there is a fine adjustment is provided here. By operating this, this can be moved in or moved out and then once the proper gap is fixed using slip gauges, this can be locked and then it can be waxed. These gauging surfaces, they are hardened. If they are stainless still, they are hardened and sometimes carbide tips are also provided, so that the service life will be more. Another advantage is here, the operator, he need not have to push the workpiece. He can withdraw this anvil and he can place it and if when he releases this lever, the anvil moves and it comes in contact. That means, there is no wear of these surfaces. So, the service life of the instrument is more. Then, coming to the taper gauges, this is a taper ring gauge to check the taper of workpieces, external taper. So, this is the workpiece. Now, we can observe here, there is a step here. Now, we have to insert the workpiece into this tapered board and then if the surface of the workpiece is between these two limits. So, this is the top surface and this is the second one which is below this. One corresponds to the go limit. This is go limit and this is no go limit. That means, the workpiece has in between go limit and no go limit, then the workpiece is accepted. Now, we have taper plug gauge to check the internal taper. So, in this taper plug gauge also, we can observe that there is a step here. Now, the tapered workpiece is like this. This is the tapered workpiece with the internal taper and we have to insert this plug like this. Now, if the surface of the workpiece is between these two limits, so this is go and this is no go has entered into the board and no go has not entered. If this is the case, this workpiece is okay. Sometimes instead of step, the two marks will be provided and this is for go and this is for no go. Go enters and no go does not enter, then the workpiece is accepted. So, one important thing in using these tug gauges is sometimes the, so this is the workpiece with the taper and then we have the workpiece like this. Now, the taper angle is more, taper is more in the workpiece, but it is laying within the two steps. The tendency of the operator is, it will simply accept. The reason is the work surface is between these two limits, but actually the taper is not okay. So, it is necessary that we have to check whether the taper is proper or not. So, for that there is a method of checking, see this indicates only the maximum size is okay, maximum diameter is okay, but it does not guarantee whether taper is okay or not. So, for that there is a method of checking a taper. So, what operator will do? He will take the workpiece and he will coat three lines on the workpiece using the pressure blue pigment. That means he will take that pressure blue, he will mark one line, second line and third line on the other side, equidistant lines are marked. And then he has to insert that into the hole and then he has to rotate the gauge maybe for 1 or 2 turns and then he has to remove the gauge and then he should check whether there is a uniform holdout of the rubbing off of the line. If it is uniformly rubbed out, then the taper is okay. If it is not disturbed, the lines are not disturbed, the lines are as it is without any rubbing off, then it indicates that taper is not okay. Now, there are some limitations of using ring gauges. They indicate only overall size limits. They indicate that the bigger diameter and minor diameter are okay. There is a possibility of accepting the out of round workpieces. That means this is the workpiece with the hole. Say there is some ovality in the workpiece and now we are inserting the gauge. So, now you can see this out of roundness cannot be detected by these ring gauges. And worker is prone to pass the workpieces with excessive taper. That means he checks whether the surface of the workpiece is within the limits. If it is within the limit, he will just accept without bothering about the taper. So, use of pressure and pressure blue will be useful in checking the taper. And other thing is workpiece must be taken out of the machine and it should be deep deburred before an effective check can be made. That means workpiece should be removed from the machine. It should be cleaned and then he will take the ring gauge and then he will try to enter it from one end. So, time taken to gauge the workpiece using ring type gauge is more. Whereas, if we use snap gauges, C type for snap gauge, without removing the workpiece, you can insert this snap gauge and you can check the size. Now, coming to the thread plug gauges, now you can see here these are used to check whether the threads are proper or not. For checking the internal threads, we use the plug gauges and for checking the external threads, we use ring thread gauges, which we will be discussing after a short while. Now, here double ended thread plug gauges. Now, you can see here this is a go end of the thread plug gauge and this is no not go. And you can see the length of the go gauge is more as compared to not go. The reason is go gauge should fully enter into the workpiece and you should check the maximum possible features like pitch and then pitch circle diameter and major diameter etcetera. Whereas, not go, they are not expected to enter into the threaded hole. So, full form of thread is not provided. Only some 2, 3 threads are provided. Another thing is as per the standard, all the details are mentioned here. This is for metric thread 16, m 16 and with pitch of 1.5 and the 6 pitch indicates the tolerance that is provided. So, whenever they are not used, not in use, we have to apply the protective coating like this. This is one more gauge with m 10, 1.5 pitch with the tolerance 6 h and again we can see the hole is provided and these are taper lock type. So, whenever these gauges are worn out, we can remove them and we can replace them. This is a thread roller gauge, C type thread roller gauge. One will be for go and another one will be not go and up to 30 millimeter interchangeable go no go thread plug gauges are used. That means, whenever they are worn out, we can replace them. That is interchangeable go no go gauge double ended and 30 to 52 millimeter reversible go no go. That means, sometimes this portion is used and this is worn out in the case of reversible type. So, the gauge is removed and then it is reversed and put into the handle. So, they are called reversible thread plug gauges and over above 52 millimeter separate go and no go gauges are used. So, we have adjustable thread gauges. That means, say the fixed type thread gauges, if they are worn out, we cannot do anything. We have to remove them and we have to use new gauges, but here we have a ring type adjustable thread gauges. If there is some varying of the gauges, we can adjust them and we can reuse them. So, once the adjustment is made, again the screw is waxed. So, that unauthorized adjustments are not carried out and this is ring type fixed thread gauge. You can see this is go gauge and this is no go gauge. This is for a particular case m 10 1.5 and this is the tolerance that is provided and this is the manufacturer detail. Again, you can see there is a group to indicate that this is no go gauge. Now, I am showing ring type thread gauges. This is m 10 1.5 pitch go gauge and this one is m 10 1.5 pitch go gauge 1.5 no go gauge. The tolerance limit, tolerance that is provided on these gauges is 6 g. Now, you can see the length of the go gauge is more or the height of the go gauge is more when compared to the no go gauge. This is the workpiece screw thread which is to be inspected. Now, the go ring gauge should go into the workpiece. It should fully enter and no go gauge should not enter. If that is the case, the screw is accepted. Now, in the go thread gauges, full form of threads are provided and here full threads are not provided. Only 2, 2, 3 threads are provided. The reason is it should not enter into the workpiece. So, there is no necessity of providing full length of the thread gauge, threads and full form of threads are also not required. This go gauge should check all the elements, most of the elements of the screw like pitch circle diameter pitch. Whereas, this will check whether p c d, this will check only the pitch circle diameter of thread. Now, we can see that there is a groove provided on the periphery of the no go gauge to indicate that this is no go gauge. The surface is nulled to provide proper grip. Now, I will show how to use the go gauge I am inserting the workpiece into the go gauge and I have to turn the screw. Now, I am rotating the screw. You can see it is entering into the go gauge. So, go gauge has fully entered into the screw. Now, I am removing it. Now, I will use this no go gauge and I will try to insert the workpiece screw into the no go gauge. You can see it is not entering into the gauge. So, go gauge is entering into workpiece and no go gauge is not entering. No go gauge is entering into workpiece and no go gauge is not entering. That means, the screw is acceptable. Now, these are the special type of coated thread gauges. They are coated with titanium nitride coating is performed on such gauges. You can see the gold color on the gauges. They have some special, this is double ended type, this is single ended type and this is again a gauge for a bigger diameter. Now, what are the advantages of such tin coated gauges? We can see here there are many advantages of tin coated gauges. So, tin coating is an extra hard surface and it has some lubricity, lubricant properties are there. So, because of that, wear life is more. So, the service life of tin coated gauges, thread gauges are more and they permit longer frequencies between recalibration because of the wear life, extended wear life and gold color serves as a wear indicator. So, with the continuous usage of these tin coated gauges, what happens is that gold color is faded out. So, that indicates that the gauges are getting worn out and then we have to replace them or we have to send them for re-coating. Now, due to inertness of the tin, they offer high resistance to corrosion. Corrosion resistance is provided, making them ideal for use when humidity and other atmospheric conditions create corrosion problems. When gauging soft materials, loading up of material on the gauge flanks is prevented due to the lubricity of the tin coating. This tin coating, it is non-stick surface against most of the materials because of that buildup problem is eliminated. Then they have the service life of the tin coated thread gauges, the last 3 to 8 times longer when compared to crown plated gauges and typical tin coating thickness varies from 0.2 to 2 micrometers. Since the coating thickness is very, very less, there is no problem of peeling off and adhesion of tin which steel is very good. Hardness of tin coated surface is 85 rockwell sea whereas, tungsten carbide and chrome plating chrome plated gauges. In the tungsten and carbide chrome plating, in that case, the hardness is 70 rockwell and if it is only hardened steel, the hardness is 60 rockwell sea whereas, in the case of tin, it is higher 85 rockwell sea and then coefficient of friction of this coating is very less 0.4, 0.6 up to 0.9. So, because of that the wear is less. Now, we will move to the wire gauge. These are used to check the thickness of metal wire and metal sheets. I can see here, this is a wire gauge made out of hardened steel and the slots and they are made like this. Now, you can see here, this is the how these wire gauges are used. They can be used to check the sheet metal thickness and then they can be used to check the thickness or diameter of the metallic wires. Now, how to use this? We have to take the workpiece, say sheet metal and we have to say insert from this side. We have to always insert, say this is the slot. Slot is like this. So, we have to take the sheet metal. So, this is the sheet metal with some thickness. So, we have to move the sheet metal in this direction. If it is rod like this, we have to take the rod and we have to move in this direction. Now, initially we have to take the sheet metal or rod and say we are trying to insert in this particular slot which is marked as 20. This indicates the gauge of this particular slot. Now, say it enters. Now, what we have to do? We have to remove that sheet or rod and then we have to try to insert into the next hole marked 19 gauge. Now, say it does not enter. So, what we have to do is, when it does not enter, we have to consider, take the previous number that is 20 in this case 20 as the gauge of that particular sheet metal or wire. Now, once we know the gauge, using the conversion tables, we can, we will come to know the thickness of sheet metal or wire. If the gauge number is 20, the thickness is 0.912 millimeter. If the gauge number is 19, it is 1.062 millimeter. As the gauge number decreases, the thickness increases. Now, this is a radius gauge, plate type radius gauge. They are available in the range of 0.5 to 13 millimeter radius in steps of 0.5 millimeter. This is a set of radius gauge and what are the uses of radius gauge? They are mentioned here. So, this radius, a particular radius gauge, it can be used to check the inside radius, this fillet and then it can be used to check the groove radius and it can be used to check outside radius, ridge segment and then roundness or diameter of the shafts. This is an angle gauge set. Different types of sets are available. This is a set with 16 pieces. You can see here, the radius gauge, there are 6 angle gauges, 45 degree gauge, 30 degree gauge, 15 degree gauge, 5 degree gauge, 3 degree gauge, 1 degree gauge. Like that, in minutes, 30 minutes, 20 minutes, up to 1 minute and in seconds, 30 seconds, up to 1 second. So, like this, totally 16 piece set and 13 piece sets are also available. What is the accuracy of these angle gauges? If it is tool room set, the accuracy is plus or minus 1 second. If it is laboratory type, then accuracy is plus or minus 0.25 seconds. Again, similar to the slip gauges, these angle gauges are ringed to assemble to the required angle. So, here an assembly is shown here, 30 degree is ringed with 3 degree to get 33 degrees. You can see plus symbol is on one side. Here it is in the reverse, plus is here and plus is here in this particular. So, 30 minus 3 is 27 degrees. So, this angle is 27 degrees, 27 degrees. Like this, to any required angle, we can assemble the gauges. Now, we have spline gauges and serrations gauges. You can see here, this is a go type spline gauge and this is a no go type spline gauge. Full form of spline is provided on go gauge and only two splines are provided on not go gauge. So, this go gauge should check all the elements like width of the spline groove and height of the spline groove. All those things, this will check. Whereas, not go will check only whether the spline width is proper or not. This picture shows how the spline gauges are used and this is a serration gauge to check the serrations. The gauges are available for to check internal serrations as well as external serrations. So, we should use in pair one for go and one for not go. Now, there are gauges like key way gauges used to check whether the key width is proper or not. For example, say we have some shaft like this with the key way like this and we want to check whether this key width is ok or not. In such cases, we can use these key way gauges. So, one end will go and other end not go will not go. So, if that is the case, the key way is proper and there are different kinds of gauges like plate depth gauge and then combined bore and face gauge and then position gauge and then length gauge over to bore. Now, you can see this is a plate depth gauge and we have to check whether this particular depth is ok or not. There is certain dimension for this depth with some tolerance. So, in that case, we can use plate depth gauges which is shown here. So, this is go side. It should go into the workpiece and no go side should not go. If that is the case, the workpiece is accepted. Similarly, we have a plug depth gauge. This is the plug. Again, this depth is to be controlled with some dimension D with some tolerance. So, this side is go side that should go into the depth and no go surface should not go into that. If that is the case, then the workpiece is acceptable and this is combined bore and face gauge. Now, we need to control this size with respect to this axis. The radius is to be controlled with some tolerance. So, in such cases, we can use combined bore and face gauge. This spindle will move into the bore and then you can see here there is a step here. This portion should go and then this surface should not go. If that is the case, then this workpiece is accepted. That means, this go is equal to r plus 0.01 and this no go is equal to r minus 0.01. It will also check whether this particular surface is parallel to the axis or not. This is a position gauge. We have to control the location of the recess. So, this is to be controlled with the dimension D with certain tolerance plus or minus 0.1 millimeter. So, in such cases, we can use a position gauge which looks like this. This is the datum surface and this is the go side. Go side should enter and no go should not enter. So, this is equal to go the upper limit and this is equal to the lower limit. Then, in some cases, we need to control the length of the workpieces. So, in such cases, this is the length L with plus minus 0.01 millimeter. This is to be controlled. So, in such cases, we can use this length gauge. So, this side it is go. It should enter and this is no go. This should not enter. If that is the case, then workpiece is accepted. Now, this is an indicating gauge. So, example is bore gauge. So, this is used to check whether the bore is within the two limits, the maximum limit and minimum limit. That means, using master's, the two limits are fixed in the bore gauge and then they can be used to check whether bore is acceptable or not. Another example for indicating gauge is a dial gauge. A dial indicator using slip gauge, we can adjust the two limits. One slip gauge for lower limit and one slip gauge for upper limit. Then, we can note down what are the pointer locations for go and no go. Then, if we insert the workpiece, if the pointer is between the two limits, then the workpiece is accepted. So, like this, dial indicator can be used as an indicating gauge. Now, we will move to air gauge. Now, in the conventional snap gauges, plug gauges, what happens is, the workpiece surface will come in contact with the gauging surface of the gauge. So, because of that, there is a lot of friction is there and then the surfaces are worn out and the sizes will vary. So, such problems will be made there. In the case of air gauge, the gauge will not come in contact with the workpiece. That means, there is no frictional problems and there is no problem of veering of the gauging surface. That is the advantage of air gauge and we can always have very high magnification like 5000, 10000, 15000. Magnifications are very small distances can be amplified up to 20000 times and a clean air is used for gauging purpose. This is an indicating type air gauge. You can see the piping to supply the compressed air. The pressure will be something like 2 bar to 5 bar. We have to use the all regulators, pressure regulators, filters etcetera to clean the air and then clean air is supplied here and the air will enter into the gauging probes. We say probes and this is a snap type probe. You can see here it looks like this. So, this is a snap probe, air probe. So, air will enter like this and here there will be nozzles. So, air will escape from here. So, when there is no workpiece here there will be air will be freely flowing and there will be certain position of this pointer. When we keep the workpiece here, now air escapement is restricted. So, the pointer position will change. Initially, using masters we can set two limits, one for upper limit and one for lower limit and then we can remove the masters and we can use it for gauging the workpieces. So, depending upon the size, if the workpiece size is within the limit, then the pointer will be within the two limits. In such cases, the workpiece is accepted. Now, this is an advanced type of air gauge, wherein RS-232C facility is available. That means, the variation of the workpiece can be stored in the computer for statistical process control and this is a air plug gauge and this is a air ring gauge. Inside, there will be pores and similarly here there will be outside, there will be pore. This plug gauge is used to check the bores. So, we have a workpiece like this with a bore and then this plug gauge can be inserted like this. So, air will be moving like this. It will be escaping from the nozzles and then this instrument will give the reading, whether the workpiece is acceptable or not that the level will change depending upon the size of the workpiece. Now, this is the air gauge circuitry. The compressed air should be supplied to the air gauge and many valves are there to control the air flow. A filter is there, a restrictor is there, a pressure regulator and then this is flexible hose and there is a pressure gauge. Now, this is the probe, air probe and then we have to keep the workpiece in front of this. Now, say we are checking this distance. If this distance is within the limit, then the pressure gauge pointer will show the, it will be within the two limits, upper limit and lower limit. Then this distance is ok. So, like this we can use the air gauge. This is the pressure gauge. When the workpiece distance is proper, the pressure will increase and then the pointer will move. Similarly, we can use the rotometer also. So, there will be air flow and there will be the float at a particular position. This is the scale of the rotometer. Now, when this distance varies, then the flow also will vary. Say this distance is x. If this distance is less than x, then the air flow is restricted. So, this float will come down. If distance is more, there is more air flow. There is no restriction. So, air flow will be more. This float will move up. Now, whether the float is within the two limits or beyond the limits that we have to see and then we have to take the decision whether the distance is ok or not. Now, these air gauges can be used for various applications like inside and outside diameter measurement. You can see here this is the workpiece and bore we have to check. So, the internal diameter can be checked and this is the shaft. The outside diameter can be checked and for average size measurement, multiple nozzles are there and then gauging out of roundness. See here gap is less. So, there will be a particular position of the float and when we rotate this probe, now the gap is more. So, the float, the position will change that indicates that there is out of roundness. Also, whether there is any loading that also can be checked. Straightness can be checked whether the surface is straight or not or any taper is there in the hole. Cylindicity can be checked. Groove width can be checked. Flatness also can be checked. We have to move the workpiece in this direction and see the because of this error, the gap is varying and then the float or the pressure gauge pointer will change. So, that indicates that there is some flatness error. Now, the different kinds of arrangements are possible. Two jet air ring gauge, three jet air ring gauge and then air snap gauge. So, this is see in the case of ring gauge, what happens is we have to push the shaft from one end. If the shaft is too long, then it becomes difficult to check the diameter of the shaft. So, we have to go to one end and then from one end, we have to move that ring gauge. So, in such cases, the air snap gauge will be very useful. At any point on the shaft, we can move the snap gauge and we can check the diameter and it is always necessary that we have to check the diameter at 3, 4 places and then we should find the average of the diameter. These are some air ring gauges. You can see the pores here and ring gauge and then plug gauges and then snap gauges. These are commercially available. Now, what are the advantages of these air gauges? Now, we should understand that these air gauges, they are non-contact. They will not come in contact with the work part. Hence, there is no problem of wear. So, the replacement of gauges and such things are not there in air gauges and these moving parts, number of moving parts are very less. So, the maintenance is also less and inertia since the probes are very light in weight, the inertia effects are also less and the measuring pressure is very small. It varies from 2 bar to 5 bar and this year, compressed year, it also helps in cleaning of the work pieces. If there is some dust particle in the work piece, the work pieces get automatically cleaned. Whereas, in the conventional gauges, metallic gauges, we have to clean the work pieces and then we have to clean the gauge and then we have to use. Whereas, here self-cleaning is taking place and it is possible to have a very high magnification and then indicating instrument can be removed from the measuring unit. Air probe can be at one point and then indicator can be at some other point. So, remote operation is possible. This is suitable for gauging diameter of holes where the diameter is very, very small compared to length and it is probably the best method for determining the vitality and taper of the circular bores. It is very easy to check the vitality and cylinder city of the bores. Now, what are the disadvantages of air gauges? See, elaborate auxiliary equipment is needed. That is, compressor is needed and filter regulator is needed and flexible hoses are needed, accurate pressure regulators are needed. So, the investment may become slightly more compared to the fixed gauges, the other conventional gauges. The scale is generally not uniform. That is another problem. Only within the short or small linear range, we have to operate these air gauges. When indicating device is glass tube, then high magnification is necessary to avoid the miniscuous error. So, we have indicator in the form of a glass tube with a hole like this and then there is some liquid which is moving. So, there will be a miniscuous error problem will be there. So, in such cases, we should go for higher magnification and operators is not easily portable and is rather elaborate for many industrial applications. So, whenever we want to move it, the complete set we may have to move and then different gauging heads are required for different dimensions. Now, let us study what are the advantages of limit gauges. These gauges can be comfortably and conveniently used in mass production to check the dimensions of the workpieces and they can be used by semi-skilled operators. There is no elaborate training is needed to teach how the gauges are used and they are very economical compared to the measuring instruments wherein they give the actual dimension. Since these limit gauges, they give the status whether it is acceptable or not acceptable and no measurement is made. So, investment in the inspection tools is very less and it is very rapid. So, the gauges can be used to check the sizes rapidly. So, inspection time is less and coated gauges have a longer life and there is no operator fatigue and high strain. In the case of measuring instrument, operator high strain is involved. He has to take the reading and sometimes he may have to use magnifying lenses. So, in such case, high strain is involved whereas, in the limit gauging such problems are not there and there are very little chances of making error. Go should enter, no go should not, then we just decide that the workpiece is acceptable and no external power is needed except in the gear gauges and less moving parts in most of the limit gauges. Hence, little maintenance is involved. Now, there are some limitations of limit gauges. They do not indicate the actual size of the component. That means, if statistical process control is required, in such cases limit gauging cannot be used and they are susceptible for wear and expansion. For example, if there is slight change in the temperature, they expand and also in the case of snap gauge, if the operator applies over pressure, then it will expand and we may get some error in the inspection and need for large space for storage of gauges and they cannot handle finer quality jobs due to precision issues that are involved and require frequent checking of gauge dimensions. Again and again, we have to calibrate. As for ASO standard also, once in a quarter, we have to inspect them and we have to calibrate them and we have to take some care while using the limit gauges and while storing the limit gauges, mask gauges, inspection gauges and working gauges. These are different types of gauges. They should be used for which they are intended. That means, working gauges cannot be used as master gauge and inspection gauges, they should not be used for regular inspection. And before use, gauging surface should be cleaned and oil should be applied and we should not over force the gauges and we should always supply rust preventive oil while storing when they are not used, not in use for a longer duration. We should always conduct proper calibration before use. Now, we will stop at this stage. We discussed about different kinds of gauges. We also discussed about the year gauges and what are the limitations of limit gauges and what type of care should be taken in using limit gauges. We will stop at this point. Thank you.