This replacement bolt on 4 hole rear spring hanger for boat trailers is made out of hot dipped galvanized steel. This hanger will work on a double eye spring, single axle trailer. Simply bolts to the frame of your trailer using 3/8” bolts. This spring hanger is used on 1 ¾” wide Double Eye spring. The bolts to attach the double eye spring to this hanger would be a 9/16” bolt. This hanger is skinnier than the front hanger to allow for the spring shackles to attach on the outside of the hanger.