Garboard Drain Plug in bronze with 1/2" diameter
For bilge drainage
Removable nut
3/8" neck depth

This Attwood Bronze Garboard Drain Plug reliably provides bilge drainage when hauling out, and it seals securely when not draining.
It has machined and tapered pipe threads to ensure a watertight plug fit, and the nut can be removed with a wrench or pliers. 
This drain plug has a 3/8" neck depth and a 1/2" NOT drain. 
It installs easily and securely using #8 screws in 3 countersunk holes.