Lots of people are starting to realize the advantages of a spring under suspension. One big advantage is that it keeps the center of the axle closer to the main leaf in the leaf spring pack. This greatly reduces the leverage placed on the leaf spring pack on vehicles with large tires and lockers so the tendency for axle wrap is greatly reduced. Also with a SUA configuration you can run a softer leaf spring with more arch which will provide more suspension travel without adding lots of lift that would raise your center of gravity. This is why all the desert guys that have leaf springs in the back will run a set of Deaver Long Travel Spring with a SUA set up. These perches are made to fit a 3 to 3.25 axle diameters but can be easily modified to fit larger axle tubes. These perches are bent for a 2.50" wide spring. Barnes 4WD Spring Under Perches are sold in pairs.