Black nylon screw type drain plug features an koi ring for positive sealing. Fine threads maintain sealing under high vibration conditions. Mounts in a 1" (2.54cm) diameter hole and mounts with two #8 screws. Mounting flange: 11/2" x 2" (3.81cm x 5.08cm). Ideal for boat transoms, fish wells, ice chests. Plug is attached and cannot be lost.