ChuckJ said:   I understand no grease on the threads, but a fire hazard?...


Oil, grease, etc can spontaneously combust in an oxygen rich environment.

Want to try an experiment - Shoot pure O2 from an oxy/acetylene torch at an
oily/greasy shop rag.  Be prepared for fire.  Thus, caution when using a
torch with dirty (greasy) jeans and don't introduce ANY oil into your o2
system.

Seems there was once even a warning about not using lipstick and oxygen
together as the lipstick had a somewhat greasy base and could ignite when
bathed in O2.  (Myth???)

Rick