Taperlock Thread Plug Gauges are designed for inspecting internal threads for rejection or acceptance of the finished threaded product. The GO end (member) is longer than the NO GO (H1) end and has a chip groove to clean out debris such as chips and dirt. Taper Shank Thread Plugs are designed to lock into taper holes in the handle.
Threadlock Plug Gauge page 221B
threadlock plug gauge