 Hello friends, myself, Prof. Narendra Katikar, Assistant Professor, Department of Mechanical Engineering, Valtran Institute of Technology. Today we are going to see the particularly knowledge about the fit designation. At the end of the session, the student will be able to read the tolerance table. The student will be able to calculate limits and tolerances. Student will be able to identify type of fit. Some of the friends, whenever we are starting with the topic limits, fits and tolerances. Let us see the prerequisite for the same. I suppose that you are revised the terminologies required for limit, fits and tolerances. For the same, we had already learned this particular basic diagram, where all these terminologies are included. For example, as we know, whenever we are applying the fit for any particular pair of combination of elements, we are going to consider those elements in the two different forms. Always the pair or engagement of the parts will be considered either a shaft or a hole. So, the tolerances will be applied considering the elements are the shaft and hole element. So, for the shaft, minimum diameter, maximum diameter will be calculated. Minimum limit size, maximum limit size will be calculated considering the basic size. This is the zero line basic size in addition or subtraction rather the arithmetic addition with the deviations. For example, the basic size minus lower deviation for the shaft deliver us the lower limit size of shaft. Likewise, when we deduct the particular upper deviation of the shaft element from the basic size will give us the upper limit size. I suppose that the same terminologies you had learned about the hole element also. So, here you can see the hatched band, which is nothing but the tolerance for the hole element and this is the hatched band, the tolerance for the shaft element. So, we had revised these terminologies in brief. Now obviously, for the type of fit also we had learned that is through the hole basis system and shaft basis system. To define and use the particularly basis system used are hole basis and shaft basis. For this, I think we have revised once again. This is the zero line or basic size line. This defines the diagram hole basis system, this defines the shaft basis system. So, this is the hatched band for hole element and the shaft tolerances is defined with the box lower limit upper limit and it varies deviates likewise. So, likewise clearance fit, transition fit and interference fit. This is the diagram explained for hole basis and this is for shaft basis system. Now, let us go with the one of the fit designation and we will try to see the calculation of tolerances and limit size with the means of tolerance table. For example, let us go pi 25 h 7 g 6. In briefly, I will explain the 25 stand for the basic size, which is the diameter as defined here, the Greek letter phi. Capital letters are defined for the hole element. H is not like as A for apple, but H stands with some particular deviation. So, standard is hole basis system. H stands for capital H rather capital letters are stands for hole element. So, H letter stands for lower deviation is zero. So, small letters are defined for the shaft element, likewise all these letters are further categorized with the grades. So, tolerance grades are there, 18 grades are there, 0, 0, 1, 1 to 16 likewise these grades are there. For example, now let us see if this is the fit designation, how I will come to know that which type of fit in existence for the same a tolerance table is there, IS code IS standard for tolerance table. So, out of that one abstract page I had brought here with the help of the same we will try to calculate limit sizes tolerances and type of fit. Now, let us see the tolerance table over here, try to read the tolerance table, it is little bit very smaller size, text is of smaller font, but let us try to understood initially what it means. So, this is the first row where you can observe particularly alphabets and suffix numbers are there. So, small letter indicates shaft element and capital letter indicates for hole element. The first column indicates the basic size from up to, now here let us go for our example, this is the first column where I will refer the row, so I have to define I have to refer the row, I have to match that basic size with the alphabets with the suffix number. Now, for example, this is our interested row over 24 up to 30, this is the basic size, the first column is for basic size. For example, 25 stands in between 24 to 30, now we have to refer this particular row and I have to check that where the lower deviations are indicated for my selected letters. Now, let us see 525, 525 row has been identified, now H7, capital H7, where is the capital H7? H7 is here, I will try to match and this is the particular rectangle box where you can found that some values are there 0 and plus 21, already I had been mentioned that H stands for lower deviation is 0, so this figure is indicating for lower deviation and this one is for upper deviation, obviously this H7 stands for our particularly hole element, so now 0 and plus 21. One more important thing, these boxes are defined some numbers, the unit is micron, 1 micron is 0.001 millimeter, 1 millimeter is equivalent to 1000 microns. Let us note down this value, now I will mention here H7 and I will write here G is 6, H7 is for upper deviation and upper deviation, this is 0 and let us see over here how much it is 21, this is a plus 21, this is the unit in micron as I said earlier, now let us go with the, now the H7 is over, now let us go with the G6, where is the G6, G6 is over here, now you can see the deviation minus 7 minus 20, minus 7 and minus 20, I had been referred this value, now let us see that how to use these values, now for that let us calculate, now conversion of these values into the millimeter, so this will be the upper deviation is 0.021 and lower deviation is 0.000 millimeter, now basic how to calculate limit sizes, lower limit and upper limit of whole, lower limit stands for basic size 25 minus lower deviation that is 0.021, it comes to be for 24, 9 and 21's means 79, this is the 25 minus lower deviation for, sorry upper deviation, for lower deviation it is 0 that means 25.000, similarly for sharp element lower limit size that is basic size arithmetic addition to particularly first deviation that is 24.993 and here 25 minus this one in millimeter, these are in micron, these are in micron 20, 24.980, now with this figure I have to draw the tolerance, I have to draw the tolerance particularly zones and I will identify which type of fit it is, this is the basic size that is 525, now what are the particularly whole sizes 24.979, this is the whole, this stands for 24.979, now what are the sizes of the sharp 24.993, 24.980, so it will be somewhere here, somewhere here 24, this is actually as like a graph 24.980, 24.993, so you can visualize here small gap is there, so I will define in a one minute that particularly upper limit of sharp is less than lower limit size of whole, so always there will be a positive gap, so which type of fit if I define with the whole basis system, so this will be the clearance fit, so this case has been defined over here, clearance fit is not it, so this is all about the limit fits and tolerances fit designation, the references are as follows, machine drawing by Siddheeshwar Shastri, machine drawing by P.S. Gill, thank you.