T-H Marine Boat Plug's are a self-retaining drain plug constructed of black polypropylene. The Drain Plug features a chemically inserted "O" ring that completely seals the plug and will not wear out over time. The Drain Plug's threads maintain sealing under intense vibration and other conditions while a special design prevents cross threading. The Drain Plug mounts in a 1" diameter hole with two #8 countersunk stainless steel screws, the back side of the mounting flange has a groove to insert sealant where it will hold and waterproof the mounting. The entire Drain Plug is 1 1/2" x 2". The Drain Plug is quick and simple to install with a design that prevents leakage and loss of the center/screw-in. Works great for boat transoms, bait tanks, fish wells, coolers, ice chests and more.