The model P625X is for recessed installation of 4-inch speakers in ceilings or walls. Companion grille Model SG-4 provides an attractive finished installation for applications where square grilles are preferred (order separately). The backbox measures 6.25-in square x 4-in (D). It is precision formed and welded 20-gauge steel. Each side has 1/2 to 3/4-in compound knockouts for conduit. Two sides include parallel slots 1-in (L) to aid depth adjustment in areas where the surface varies in material, depth or evenness. Slots may also be used for attaching channel rails (order separately) in suspended tile ceilings. Each corner features a mounting tab with 8 to 32 screw retaining U-clip for grille installation. The backbox is coated with a metal deadener to eliminate acoustic and mechanical resonance.