Last month’s Tip illustrated how to inspect a feature of size in accordance with Rule #1 of the Y14.5 Standard. If size is inspected correctly, the geometric form (straightness, flatness, circularity and cylindricity) of the feature must be within the total size tolerance. Therefore, form controls are usually not necessary.
If for example, two point checks were made on the Ø 2.000 ± .005 and it measured 2.005 everywhere (which could only be possible in theory) and it could fit a ring gage of 2.005, this pin would have to be perfectly straight, circular and cylindrical. If production produces this pin smaller than 2.005 (MMC) straightness, circularity and cylindricity are allowed, but may not exceed the total size tolerance of .010.