Attributes . Welded steel construction; 3-3/4 in. square x 3-1/2 in. deep; Painted red for dedicated life safety alarm systems; 3-3/4 in. opening in wall allows for margin of error when using a 4 in. square cover; Accepts standard 4 in. square covers; Supplied with sixteen 1/2 & 3/4 in. concentric knockouts; 40.5 cu. in. capacity; Acceptable for use in 2-hour fire rated walls . Names