These drain plugs are designed with a molded-in recess in the base, trapping sealant in place and providing a more water-tight seal. The integrated captive mechanism keeps the plug attached to the boat even when unscrewed, lessening the chance of lost plugs, but we include a spare plug standard just in case. Includes 2ea #6 3/4" flathead stainless steel screws for installation Replacement plugs:Choose from Fine-thread (black gasket): these fit the plugs we shipped prior to Autumn 2023 and Standard thread (red gasket) which fit our current plugs. If you have any questions, please email! Injection Molded Nylon, Fine thread designHole size (A): 1" Screw spacing (B): 1-9/16" OCColor: Black Made in USA