Funny you should ask. I have an 89 4x4 blazer with a 6" lift and the rear springs came factory with about a 4 degree shim in the spring pack. The problem with it is that the springs are 2 1/2" wide but the shim is only 1 7/8" wide and I also run a hollow 3" block that is 2 1/2" wide so the shim has broke in half on the drivers side and shattered on the passenger side. The shims are made of cast aluminum. I currently have a friend making me 5 degree shims out of 2 1/2" wide steel that are the full length of the blocks.