dpb wrote in :

It's just a standard compression fitting. The flare is a compression
sleeve; the tubing will get compressed slightly and then flare some

Thanks for the explanation. That makes it much clearer.

Can I re-use the compression threads as a non-compression kind of adaptor?
Such as if I put teflon tape on the compression threads, and screw some
kind of adaptor onto them, so the water will go through the inside, with
nothing compressed?