833 Features: -Square blank box cover with knockout. -Material: Steel. -Covers are used to close an outlet box. -Raised covers are used for mounting lighting fixtures. -Raised device covers are used for mounting switches or receptacles. -Angled mounting slots compensate up to 12" for box misalignment. -Extension rings provide a means for adding additional cubic capacity or as an outlet box for surface conduit. -Red boxes, covers and extensions for dedicated life safety alarm circuits. Specifications: -4" Diameter. -Dimensions: 4.69" H x 4.69" W x 0.06" D.