A red cast-metal back box measuring 4.75 in. x 3.25 in. x 2.25 in. (12 cm x 8.3 cm x 5.7 cm) with ½ inch (12.7 mm) knockouts in the short sides. The back box is UL listed under UL38 and is UL certified for use in Canada. It has been approved by CSFM (7150 1615: 224) and NYC/MEA (382 94 E, Vol. VI).