This replacement bolt on rear spring hanger for boat trailers is made out of hot dipped galvanized steel. It Directly bolts to the frame of your trailer using 3/8” bolts. This spring hanger is used on 1 ¾” wide slipper spring. The bolt to attach the slipper spring to this hanger would be a ½” diameter Leaf Spring Mounting Bolt. We have 3/8" Diameter Trailer Bolts available in stainless steel and zinc plated for mounting this hanger to your trailer. Typically, this hanger would be most common on C Shaped channel trailer frames. This is the Rear Spring Hanger because the inner width of the hanger is the right dimension to accept the rear slipper Spring.