In article , Peter T. Keillor III
says...

Well, here's one vote for just plain 'ol teflon tape. I've
used it for years, for all kinds of gas/water/vacuum applications,
and never had any trouble with it.

Properly applied it will produce a helium mass-spec leak tight
connection with NPT fittings - brass, stainless, copper, or
any combination of the above.

The other kinds of pipe dope compounds work too, like the SWAK
with PTFE particles in it. But I find the teflon tape to be
neater and more reliable.

Except with stainless on stainless. It doesn't always prevent
galling. The stuff for that is Loctite PST.

I've used it for stainless on stainless NPT fittings. You are
correct that it is unwise to try to dismantle and re-use that
combination - but a properly made-up fitting set like that
will seal just fine with teflon tape.

Jim


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