This is a heavy duty replacement hot dipped galvanized leaf spring hanger for magic tilt trailers. This 4 hole bolt on center hanger is for use with 1 3/4 inch wide springs and is used as the center hanger on the trailer frame. It attaches to the aluminum I-beam frame using 3/8 inch diameter bolts. Typically a 1/2 inch diameter bolt is used to attach the leaf spring to the hanger. Magic Tilt part # PK1800. If you are needing 3/8 inch Mounting Bolts for this Magic Tilt Leaf Spring Mounting Bracket check out Boat Trailer Bolts