Shim-lock mounts residential and commercial wiring devices flush, regardless of wall condition. Fasten it onto screw in mounting slot, and tighten to the desired depth. Shim-lock tabs secure the screw, preventing floating installation Made of steel with a heat-treated finish and clear zinc chromate plating, it is 0.310-in. in length with a #6 screw opening. In addition, it makes adjustments from 1/8 in. to ¾ in.