GSG Thread Plugs

A thread plug GO gage checks the minimum major diameter and the minimum pitch diameter size in a part, while the NOGO checks for the hole not to exceed the maximum pitch diameter size in a part.

All GSG thread plug gages are manufactured to ASME/ANSI B1.2 or B1.16M and are all made of oil-hardened tool steel.

Thread Plug Styles


  • Reversible Thread Plugs – Available up to and including 19.05 mm. Thread plug gages can be reversed end-for-end in the handle, which results in double the wear life. Each end of the handle is color coded (green for GO and red for NOGO). Chip grooves are provided on both ends of the GO work plug member #10/M4 and larger.
  • Trilock Thread Plugs – Available for 19.05 mm and larger. Thread plug gages can be reversed on the handle resulting in a longer wear life. Additionally, Trilock thread plugs provide a single-end on a handle which reduces weight with large sizes.
  • Taperlock Thread Plugs – Available up to and including 38.1 mm. Taperlocks are the most popular style in thread plug gaging.
  • Taperlock Set Plugs – Set plugs are used to set thread rings for proper fit and feel and inspect the ring for wear. Set plugs have a common pitch diameter along the thread length of the GO or NOGO section. The crest of the thread is truncated for the first half of the set plug and full-form the remaining length.
  • Helical Coil Plug Gages (STI) – Helical coil plug gages are used to inspect a hole prior to inserting a screw thread insert when repairing a threaded hole.
  • Hole Location Plugs – Hole location gages are available in two types. When checking the location of a small tapped hole, the Flex Plug is used. When inspecting a larger hole (generally over 1.00 mm) the Lead Lock is used. Both gages locate on the flank angles of the tapped hole. Lead locks can be used in conjunction with the zero spindle and are a perfect way to inspect features for run-out to the pitch diameter of the thread. Special designs are available such as true position of threads to bore diameters with dial or digital indicators.