Stabilizes anchor chain and reduces stress on windlass. The two holes are used for a bridle application with two Bow Shackles (147212) for connecting lines to port and starboard cleats. Fits anchor chain sizes: 5/16", 3/8", 7/16" and 1/2". A 5/8" B 2-1/4" C 3" D 4" E 5/16"