Cylindrical ring gages have a number of inspection purposes. They are used as Go/No-Go gages to inspect the outside diameter of a shaft or rod. They are masters for dial bore gages, internal micrometers and coordinate measuring machines (CMMs). 

Screw thread inserts (STI) require the threaded hole to be inspected prior to inserting the threaded insert or coil. The dimensions and tolerances for the gages used to inspect these threads have been a bit confusing over the past 30 years. 

Selecting gages and other types of measuring tools can be challenging. It does not matter if you are an experienced or novice gage user, tool crib manager, lab manager or buyer. 

Thread classes for product threads, and by extension the gages used to inspect them, can become a bit of alphabet soup. Some find the requirements confusing.

The measurement of the depth of a hole sounds straightforward and simple. In many cases it is. In others, there are design features of both the part and the gage that must be considered to insure an accurate measurement and a properly assembled or functioning part. 

External thread inspection can seem confusing and, in some cases, frustrating. There is a wide variety of inspection tools available for external threads.

How do you measure an internal thread on a part? How do you decide what you need?

The measurement of a drilled, reamed or formed hole depth may be inspected in a wide variety of methods. 

Working thread plug gages are the fixed limit functional gages used to inspect product threads on a pass/fail basis.

The use of the go/no-go fixed limit gage is considered one of the simplest forms of pass/fail attribute inspection.