What is the difference between diametric tolerances and circumferential tolerances?
When measuring diametrically by scale, all diameters measured in a given plane must fall within the tolerance band. The resultant out-of-round can be no greater than the sum of the plus and minus tolerance. When measuring circumferentially, you take a series of diameter readings in a given plane, add them all together, and take the average. The average diameter must fall within the specified tolerance range. Or you can get the same result by measuring with a pi tape that measures the circumference and converts it to a equivalent diameter. When using this method, you must also have a maximum out-of-round. Since some diameters can be over or under the specified diameter and tolerance (but average within), you must also take the difference between the highest and lowest reading and this out-of-round cannot exceed that specified.
