These steel shims are designed to change your pinion or caster angle on a leaf spring suspended vehicle. These shims are 2", 2.5”, or 3" wide. They are CNC machined from mild steel, Silver Zinc Plated and have a 5/16” center pin hole milled into them (3" shims all have a 3/8" center pin hole). If you have larger center pins, simply drill the center hole out. THESE SHIMS ARE DESIGNED TO BOLT INTO YOUR LEAF SPRING PACK! You will need to clamp your springs, remove the center pin, and bolt the shim into the spring pack! If you are using these shims on a front axle, please read the paragraph on the 'Learn More' page about “Caster Angle.” We offer these shims in 2, 4, 6, and 8 degree sizes. Axle shims are sold seperately, not in pairs.