The constant wear and tear from rough roads and heavy loads can cause standard shackles to simply wear out. The heavy duty shackle kit is an excellent upgrade for your running gear and the answer for wear and tear.
9/16" x 2.90" Shackle bolt with 7/16"-20 threads with nuts. For use with spring hanger brackets and equilizers. Fluting prevents the bolt from turning, which can wear hanger brackets.