Washing machine outlet boxes, ice maker boxes, tub boxes and service boxes, with the brackets and covers that go with them.
An outlet box recesses the valve and the drain into the wall cavity so the appliance can sit flat against the finished surface. Without one, the appliance stands off the wall by the depth of the hose and the stub-out, which on a laundry pair is enough to keep the door from clearing an adjacent wall.
Match the box to the wall before ordering. Depth has to suit 2x4 or 2x6 framing, and the connection has to match the rough-in already in place — sweat, PEX crimp, PEX expansion or push-fit. A box with an integral valve saves a joint; a box without one lets you use the valve you prefer.
On laundry boxes, a model with hammer arrestors built in is worth the difference. A washing machine solenoid closes fast enough to bang a line that has no arrestor, and adding them later means opening the wall you just closed.
