Boxes, Square Box Extension Rings and Thru-Ring with knockouts, Appleton, Type: 4", 1-1/2" Deep, Welded, Top: two 8-32 screws, Bottom: cutout for switch or handy box, red box option, Volume: 21 Cubic Inch, Sides Knockout: 8@1/2", 4@3/4", UL Standard: 514A