For quick and accurate measurements of internal and external diameters of retaining ring grooves, o-ring grooves, and undercuts. Precision machined from steel, hard chrome plated for extra wear resistance. Fits all 6" vernier, dial and digital calipers with a maximum jaw thickness of 0.140". Measures internal grooves from 0.200" up to the capacity of the caliper. Size Min Bore A Width B Max Depth C Groove Depth D 2 0.300" 0.015" 0.625" 0.070" SaveSaveSaveSave