The WJ's rear suspension uses a 3-Link design with an upper wishbone to locate the axle. This wishbone attaches to the axle with a large stud that looks like a ball joint. This stud has a limited range of movement and will bind with lifts over 4". Rusty's Upper Wishbone Spacer relocates the wishbone's attachment point on the axle and relieves the joint's operating angle. It is designed to work ONLY with lifts of 4" and higher.