A workshop identification kit spanning 16 sizes, aimed at the everyday problem of an unmarked port on an engine, gearbox or fuel component. Performance plumbing mixes AN flare, NPT, BSP, ORB and metric threads, and several of them are close enough in diameter to fool the eye. Rather than guessing and cross-threading an expensive housing, you offer up gauges until one seats cleanly and you know what to order. It earns its keep in a workshop building custom fuel systems, turbo oil lines or oil cooler plumbing, where a single misidentified port costs a return shipment and a lost day. Keep it with the tap and die set.