Gas-tight fittings

[newshound]

In the real world, it is not infinitely reusable.

[Roger Hayter]

FWIW if this connects to another piece of pipe with female connector I'd call it a union. Doubt if that helps.

[Cursitor Doom]

The locking collar's threads will wear out long before the actual sealing surfaces I would imagine.

[PeterC]

I once was looking for a book on Tribology in the Engineering section of a library - eventually found in Science Friction.

[newshound]

One strength of the design is that if either of the surfaces get damaged, say by a bit of grit, sealing can usually be recovered by giving it an extra tweak the first time. There *is* plastic deformation there.

[Cursitor Doom]

Do you really think so - about the plastic deformation? I find (certainly on my much larger hydrogen regulators which use the same principle) that they only need to be done up not much beyond finger-tight to fully seal. We do tighten them up properly, of course, but that's more to do with ensuring they don't accidentally come undone again. It's hard to visualise hard metal lumps like that deforming under such minimal pressure! But you're the expert, so I bow to your superior knowledge on this one, Newsy.

[newshound]

Hint. Take a look at them at the nanometer level.