Hex gages can be used to inspect wrench openings and spark plug wrench openings. If you need to inspect machine head fasteners or ensure hexagon holes of parts have been machined properly. Go/NoGo Hex plug gages are manufactured to ASME B107.17M and ASME B18.3. Hex Plug gages can be marked with your tool number. Go/NoGo Assemblies include 1 line (up to 25 characters) of custom marking.