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Limits of Tolerance
Effective Diameter - The tolerance is the amount of variation
allowed in the manufacture of the tap. This tolerance is added to the
minimum effective diameter to establish the maximum effective
diameter.
It follows that:
Basic Effective + Oversize
= Minimum Effective
Basic Effective + Oversize + tolerance
= Maximum Effective
The effective diameter can only be measured with special tap
measuring equipment.
Major Diameter - The minimum major diameter is established by
adding the oversize allowance to the basic major diameter (the
nominal thread size). Therefore, onmeasurement, themajor diameter
of the tap is larger than the nominal thread size, and must not be
used to judge the size of the tap.
The maximummajor diameter of the tap is governed by the thread
form and is therefore not subject to a tolerance.
