A thread plug gage is used to check the correctness of the pitch diameter of an internally threaded part, such as a nut. It is designed to inspect the functional thread and pitch diameter, and to check pitch diameter limits and the outside and inside major diameter on threaded parts. A thread plug gage is typically double-ended, with one end carrying the GO gauge and the other end carrying the NO-GO gauge. The GO gauge should pass through the entire length of the nut without requiring too much rotational force for acceptance of the part. The NO-GO gauge can enter into the nut at most over two turns and not beyond.
On the other hand, a cylindrical plug gage is used to check whether a given dimension, such as a hole, is too large or small. It is used to check a drilled hole or the minor diameter of a threaded hole . Cylindrical plain plug gages may be used for gaging hole sizes to determine if the hole is within the upper and lower limits of the product tolerance. The hole size can be determined by using go and no go plug gauges. The go gage is used to verify the low limit. The no go gage is used to verify the upper limit.
In summary, thread plug gages are used to inspect functional thread and pitch diameter on threaded parts, while cylindrical plug gages are used to check whether a given dimension, such as a hole, is too large or small.
