MORRIS 21792 TYPE S KNOCKOUT SEAL WITH SCREW AND BAR, 1"Size: 1”Steel Snap In Blanks - For use in closing off unused openings in boxes or panel boards. For use in closing off unused openings in boxes or panel boards. All steel construction provides installation integrity. Snap-Fit Design.*Type S Knockout Seals with Screw & Bar - Set screw/bar type knockout seals are inserted in open box knockouts to protect exposed wires.*Set screw/bar type knockout seals are inserted in open box knockouts to protect exposed wires*Used in standard, air tight or dust tight applications*Pre-assembled screw and backer bar slides on open knockout holes without removing box devices or covers*Steel Galvanized