This is pretty much our standard U-bolt for 3 1/4" diameter axles but square. They are .625" (5/8) rolled threads for extra strength and the threading is 5" long so they will fit! Cut off what you don't need after they are on, and they are also Grade 8. If they fit use them (if they don't fit drill your plates until they do)! All of our U-bolt Plates are recomended to use 5/8" U bolts. Comes with tallnuts and thick cut 1/4" washers. U-Bolts are sold individually.