Question about compression fittings

[toller]

A few days ago I posted a question about repairing a burst 3/8" soft copper pipe. Today I posted a question about some water filter housings I bought at an auction. Amazingly, the questions converged, because in one of the boxes was a bunch of fittings; including several 3/8" compression unions!

There are plastic and brass rings to go on the tubing. I am guessing the brass are for copper, and the plastic are for plastic. Is that correct? There also little lipped brass tubes; they go in plastic tubing? Can I use these with PEX?

[roger61611]

I think what you state is correct but you might consider buying/borrowing a good book on plumbing.

[Edwin Pawlowski]

The ones I bought are a gray plastic and specifically say they can be used with pex or copper or cpvc. I don' tknow about the others, but if the od of the tubing is the right size, I suspect they would work but can't say for certain.