We have a Dryer Outlet with the original box and screws. It was from Arrow Heart and I believe it is bakelite. The box reads "flush dryer mount for deep wall cases or 4" sq. box with cover 30A 125-250 V. It measures about 4" in H x 2 3/8" across the widest point on the top of the metal bracket with the center of the round outlet measuring about 2 1/8" across the center x about 1 3/4" in depth.

Dryer Outlet Deep Wall box nos Vintage