American Automotive steel lift blocks are stronger than aluminum. They are designed to increase rear load and towing capacity. American Automotive u bolts are manufactured for maximum clamp force and are guaranteed for life. Made of cold drawn certified 1541 carbon steel OEM factory material with grade 8 hardware, American u bolts embody extreme strength and maintain OEM handling characteristics. American u-bolts provide an even distribution of pressure to protect against premature spring failure and unwanted movement. Allowances need to be made for all overloads and aftermarket leafs.