Abstract: A foldable, electrical box kit for on-site assembly and installation in wallboard, with at least two opposing panels each having a pair of spaced apart front face flanges and respective, laterally centered on the panel, center-bored, retaining screw and rotating retainer clip assemblies. The unfolded box is configured with living hinge lines to permit easy folding and snap assembly of adjacent sidewall edges to form a rigid enclosure. Retainer clips are retracted by their retaining screws into clip slots in the panels for clearance. The box is inserted through wallboard as far as the front face flanges permit, then the retaining screws are rotated, the first quarter turn of which rotates their respective retaining clips from the retracted position to an extended position behind the wallboard. Further clockwise rotation of each screw brings its retaining clip forward into a firm, three point grip with its respective pair of flanges on the wallboard.