Work Plugs, Rings Inspect internal and external threads with Vermont Gage thread gages. Vermont Gage thread gages are made to precise class X tolerances and come standard with a Certificate of Accuracy. Standard thread plugs include pitch diameters for 2B, 3B, (inch) and 6H (Metric) class of fit. Standard thread rings include pitch diameters for 2A, 3A (inch) and 6g (metric) class of fit. Go/NoGo plug double - end assemblies get 1 line (up to 15 characters) of custom marking. Thread members are made of steel (chrome plated gages for added wear resistance are available; please inquire).