Skyjacker Blocks and U-bolts: Skyjacker utilizes blocks and U-bolts in its kits to provide rear lift. The Skyjacker U-bolts are e-coated for corrosion resistance. These U-bolts are offered in various shapes and sizes such as square, round, and semi-round in lengths ranging from 1.75 Inch To 19 Inch. The blocks used in Skyjacker kits are ductile iron with fixed center pins. They are also tapered to correct pinion angle and prevent driveline vibrations. Available in 1.25, 2, 3.5, 4.5 and 5 Inch. Rear block and U-bolt kits are usually used to make a ‘kit’ in a Skyjacker suspension lift. But a ‘kit’ could also be a combination of blocks and U-bolts or Add-A-Leafs.