"Christian McArdle" wrote in message
...
2. It seals the thread. This can prevent a leak should any water find
it's way between the outside of the olive and the main body of the
joint. I agree that in theory a compression joint should be perfectly
machined but in a lot of cases they aren't.

I'd rather know about it and discard the fitting (I've not come across one
yet).

If you seal the threads, then you won't know you've got a dud. At least
not
until a few weeks/years later.

I assume you are both on about wrapping PTFE on the thread and nut of a
compression fitting. That seals sweet FA. Thee is a gap between the nut and
the pipe. What is can do is stop the nut from running up to the olive
fully. You always know a DIYer when PTFE is used on compression/copper pipe
joints.