We make the 4°, 6° and 8° shims from solid steel for maximum durability. Designed to handle the rigors of trail use, these shims actually become part of the spring pack using the center pins provided with your leaf springs. Many other shims on the market float between the spring pack and the spring perch reducing the engagement of the center pin. Our design will not come loose or fall out. Can be used front or rear to set pinion angles. 2.5" wide springs only.