Brass Adapter, 1/4-18 Female NPT To 1/4-18 Male NPT, Straight

The 1/4-18 threads on both ends are NPTF, which means they're cut to a tighter tolerance than standard NPT and are engineered to seal on the threads themselves without tape or compound. That said, some folks still apply a light wrap of PTFE on the male end out of habit, especially in gas or instrumentation lines, and there's no harm in it. For most hydraulic and grease applications though, the thread form alone handles the seal.

It's suitable for use with fuel, LP, and natural gas systems, but only if you order it specially configured for those applications.

Built for exactly that kind of hook-up, it’s a straight brass adapter with 1/4-18 female NPT on one end and 1/4-18 male NPT on the other, using NPTF threads on both sides.