: : When installing the mixer, the should the face of that black plastic piece be flush with the fiberglass side of the shower? In other words, do I cut a 6" hole in the unit? Also, are there any standard heights (on center) above the floor for the spout and the faucet handles?

: : Any insight is appreciated. This will be an expensive one to screw up! Happy holidays.

: Reply:
: The size of the hole does not need to be six inches in diameter, only large enough for the shower faucet stem and trim to fit through, you could always make notches in the fiberglass if the faucet will have integral shut off valves.
: The plastic round piece should have writing on it instructing the installer where the face of it needs to be, there is usually a range of distance.
: The height of the valve body is 12" from the tub rim, the spout is 4" from the tub rim and the shower head about 80" from the tub floor.
: Good Luck & Happy Holidays. e-plumber

As a repair plumber I have always felt that the hole should be large enough to replace the faucet later if need be. And that some escutcheons are indented in the middle to set back into the wall to keep new installers from cutting too small of a hole. The plastic piece is for rough-ins to have the finish wall come up to it.
The plastic trim piece usually fits tight against the shower and some use it as the back support piece instead of the preferred backing brace. LonnythePlumber