Thread gauges are dimensional instruments for measuring or verifying thread size, pitch or other parameters. A variety of thread gauging instruments and tools exist such as measuring wire, tri-roll comparators, thread plug gauges, thread ring gauges and thread micrometers. The appropriate variable or fixed limit gauge for an application should be selected based on internal and external thread type, specific thread designation such as UN thread gauges and UNC thread gauges, part tolerances and gaging frequency. Thread gauges can be any number of types of gauges such as UN and UNC thread gauges. 

These include plug, ring, 3-wire, micrometer, tri-roll comparator, measuring wire, screw thread gauges, roll thread gauges. There are many unique thread types, profiles and geometries which provide different usefulness. Such thread designations such as UNC thread gauges and UN thread gauges as well as others such as UNEF, UNF, NPT, NPTf, NPSF etc. are thread gauges measured in size or diameter of the feature that is being measured. English pitch is the threads per inch that the gauge can measure. Metric pitch is the metric thread spacing that the gauge can measure. However UN thread gauge types are the ones with specification of the shape and dimensions of the thread for a given size (diameter) of fastener and the number of threads per inch (note; thread per inch of fastener length.) UN bolts and machines screws are the types of the fastener in everyday use in major countries. 

On the other hand, UNC thread gauges are special case of UN. For every UNC thread size, the UNC detailed description also indicates how many threads per inch the fastener should have. Most hardware stores in some countries will sell UNC fasteners. There is a slight difference between UNC (Unified Coarse) and UN. For each UNC thread size, the UNC specification also indicates how many threads per inch the fasteners must-have. Thread verifiers, thread detection probes or thread verification systems detect or verifies the presence of threads, threaded holes or specific thread pitches. 

Thread authentications mostly make use of high speed, non-contact technology to rapidly inspect parts. Also common shapes or geometries measured include cylindrical and tapered or pipe. Also a go gage renders precision machinery for the production of a comparative gaging based on a fixed limit. As regarding the measurement as explained above as both English and metric can be used. The unveiling on the gage can be known- graduated meaning that the gage has no display dial.