After removing from the dash, there are 3 pins holding the rear ring on. Using a flat chisel, I carefully tapped the rear ring off the pins. On re-assembly I tapped the rear ring back onto the pins, then used a punch to spread the pins back out to make sure they held securely. My 2nd vent actually had the pins replaced with 3 small screws, there were remnants of the pins still. I never knew anyone had my dash apart before.