5/16" (8mm) Racelite Rail Mount Block
Any time you need a fixed block attached to the rail of a boat, you may be able to use this one. It can be used to raise a flag or banner, for a jib sheet, topping lift, or gravity shower, or any of dozens of uses.
Complete with bushing to fit any standard rail, it's 1-1/6 sheave will handle up to 5/16" line. Stainless steel and plastic construction will withstand salt water environments.