A gem box is the standard steel switch or receptacle box, about 2 by 3 inches across the face and 2-1/2 to 3-1/2 inches deep, with screw-on sides that come off so two or more boxes can be joined into one multi-gang box. It comes with ears, nail-on brackets, cable clamps or plain knockouts for conduit. Its weakness is volume: a 3 by 2 by 2-1/2 inch box holds 12.5 cubic inches, enough for only a handful of conductors under box fill rules.
Pull those gem boxes, there's six twelves and a device in there, put a four-square with a mud ring instead.
Box fill counts every conductor, each device as two, and all the grounds together as one; a gem box runs out of room faster than anyone expects.
Also heard as
- gangable box
- gangable switch box
Related terms
Four-square box
Square steel box, 4 inches on a side, that takes a mud ring or cover and serves as the workhorse junction and device box.
Handy box
Small surface-mount steel utility box with rounded corners, used for exposed switches and outlets on block walls.
Battleship
Thin metal F-shaped clip that holds a cut-in box in drywall by gripping the back of the wall.
Old work box
Box made to fit into an existing finished wall or ceiling through a cut hole, without access to the framing.