Best-in-Class Three Cubic Foot Back Box for 12 Models. Rectangular with Extra-Thick 16 Gauge Metal and Heavy Duty MDF Reinforcement on Top and Side Panels.Fits Control 321C, 321CT, 322C, 322CT & 321CS. 23.1" x 18.2" (20 Incl. Side Tabs) x 12.8" Deep. NOW UL LISTED Priced as one pack; one pack contains 2 Pieces)