Hello

I have 3/8 plastic tubing to connect my faucets to the existing stops. At the faucet end, I have a rubber cone washer w/ a brass ring. Is this a national plumbing approved connection?

The brass ring leads me to think this is a compression fitting not suited for plastic but the rubber cone doesn't sound like compression. My onlt thought since I can't see what you have is to take the tubing and the nut, ring and cone to the hardware store and show it to the fellow in the plumbing aisle.