Switch box extension allows a way to work with a box set too deeply in the wall. The extension slips inside any 3" x 2"switch box and fastens to the device ears with extra long screws supplied with the box. Will extend the switch box from1/4" to a maximum of 5/8". Can also be used in a single device cover on a 4" square box and, by bending the open sides,2 rings can be used in a 2-device cover on a 4" square box. UL listed.