Three piece Knock Out seals are used to seal up holes punched in panels or knockouts from outlet boxes. They are held in place by a screw inserted through the seal into a threaded strap on the opposite side of the opening. Available in sizes from 1/2 in thru 6 in. Three piece Knock Out seals are embossed to centralize in knockout. Installs from the inside or outside of any box without rearranging wires. One screw secures unit. Size is stamped into seal.