This International Standard gives the necessary instructions for the manufacture and use of gauges for checking ISO general purpose metric screw threads complying with ISO 68 and ISO 261.

It is recognized that other methods of checking may be used, for example measurement with indicating instruments. Checking with gauges in accordance with this International Standard is always decisive.

The aim of this International Standard is to provide means of distinguishing between workpiece threads that comply with the limits of size and those that do not.

In order to ensure the interchangeability of workpiece threads and to avoid disputes between manufacturer and purchaser, the following principles should be applied:

a) the manufacturer shall not deliver any workpiece thread the actual thread size (for example the pitch diameter and the virtual pitch diameter) of which lies outside the specified limits;
b) the purchaser shall not reject any workpiece thread the actual thread size (for example the pitch diameter and the virtual pitch diameter) of which lies inside the specified limits.

In order to satisfy these two principles, this International Standard establishes the requisite types and sizes of gauges for the checking of screw threads, the conditions under which these gauges are to be used and rules for the inspection of the workpiece threads.