Pin, plug, and ring gauges are used to test plain or threaded parts to determine if they are within acceptable tolerance ranges of the nominal specified size. Plain pin or plug gauges are used to test the tolerance of smooth holes and bores. Threaded plug gauges inspect internally threaded parts and pipes. Threaded ring gauges inspect externally threaded parts and pipes. Go/No-Go gauges, also known as Plus/Minus gauges, test the lower and upper tolerance of smooth and threaded straight parts, while tapered pipe-threaded products are similarly tested with L-1, L-2, L-3, and 6-step gauges. Plug gauges are used to inspect fastener threads and straight pipe threads as well as internally threaded parts or pipes. Ring gauges for fastener and straight pipe threads are used to inspect externally threaded parts or pipes.