These are designed with the standard 3" Full Sized Ford Leaf Spring in mind but will work great with a spring anywhere from 2.75" to 3" in width. These will fit an Axle of 2.5" to 3.5" in diameter. All of our U bolt plates have 3 spring pin location options. They are .375" HR P&O Steel plate and can work with .5625" (9/16) to .625" (5/8) U bolts, we recomend 5/8", why use a lighter piece of steel when you don't have too? These are sold in pairs.