Welding/cutting torch packing seals.

[Highpower]

Yeah, the old stuff was graphite impregnated, now I guess they've gone to Teflon. While it might be great for plumbing I don't know that I would trust it for compressed gases since there will always be gaps somewhere between. They used to use rope seals for the ends of crankshafts in cars. (Main seal & harmonic dampener) Fine when they were new, but get a few miles on them and they would shrink...

Glad those days are over.