Heavy-duty Carry-On Trailer Spring Shackle Bolts and Nuts are used to connect the spring inside the spring hangers. The spring shackle bolts are made to do this job with special nuts that prevent them from backing off the bolt. Each pack includes four shackle bolts and nuts each. The spring shackle bolts measure 3 in. x 9/16 in. Carry-On Trailer is the largest trailer manufacturer in the world offering a broad line of replacement parts for light and medium duty trailers. We are American owned and American built with award winning customer service. Our replacements parts are OEM replacements for Carry-On trailers and fit most other utility and cargo trailers rated at 2,990 lb. Gross Vehicle Weight Rating and below.