My Moen "single handle exacttemp 3/4 inch thermostatic valve" has a plastic ring (I belive) called a plaster or drywall ring for setting the depth of the valve below the drywall/plaster/CBU etc. I used the ring to install the valve in the wall then removed it. The instructions (picturers really) from Moen don't clearly show removing or leaving the plastic piece in place.
Does this ring serve anyother purpose besides setting the valve depth in the wall? It seems like it would block servicing of the valve if it is left in place - so I removed it.