Extension ring for 4 In. Octagon Box, 2-1/8 in. Deep, 21 Cu. in., with Concentric, 1/2 & 3/4 in. KO (50-Pack). Combination screw heads provide for faster installation, Self-tapping screws virtually eliminate stripping Specifications Width 4" Height 4" Depth 2-1/8" Material Steel Shape Octagon Bracket Type Exterior Ring Knockouts (2) K, (2) 1/2" UPC 626463002254