[ReelMagic]

The raw water strainers are manufactured by GROCO (ARG series). I to have broken the drain plug off specifically when overtightened..... Learned they don't have to be to tight to be closed. They have an "O" ring to help them seal. In any case they use to have a hex head but were changed to square to prevent anyone from using a wrench to tighten....... Believe any good marine store can get you the parts. That has been my experience. Assume WEST MARINE could get them for you.... Believe they are 1/4 x 20 thread......  I carry a spare just in case I break one during servicing.