Hose Fittings, Barbs and Quick Couplers

Thread type, size and hose inside diameter

Three things must match: the thread standard, its size and, for barbs, the hose inside diameter. Tapered threads such as NPT seal with tape or paste, while parallel threads such as BSPP or G1/4 seal with a washer or O-ring, and mixing the two leaks. A barb fits hose of the same inside diameter and needs a clamp. G1/4, a quarter-inch parallel thread, is common on liquid-cooling fittings for computers.

Quick couplers: plug and socket profiles, materials and pressure

A quick coupler is a pair: the plug on one side and the socket on the other, and both must share a profile or they leak or refuse to lock. Brass suits air and water, stainless steel suits harsher fluids, and plastic suits light duty. The pressure rating should be above your working pressure. Packs of a dozen are common for small fittings. Not everything here is plumbing; some titles are RJ45 jacks or memory-card sockets.

Questions about Hose Fittings, Barbs and Quick Couplers

What is the difference between NPT and BSP threads?

NPT is the American tapered pipe thread, while BSP comes in tapered and parallel forms with a different thread angle and, in most sizes, a different pitch. They look similar but do not seal properly together, so identify the standard before ordering.

Do I need thread tape on every fitting?

Use PTFE tape or paste on tapered threads. Parallel threads that seal with an O-ring or a washer should not be taped, since tape can stop the seal seating. Check the fitting's description.

How do I choose the right barb size?

Match the barb to the hose inside diameter. A loose fit leaks and a very tight one can split the hose, so measure the hose, push it fully onto the barb and secure it with a clamp.