Made using 7075-t6 material and polished. This system is designed to transmit the energy of a crash around the blocks and take pressure off the bulkheads. The "d" block is locked into the the rear end from the bottom to ensure that nothing can move. The lock nuts prevent the blocks from spreading and putting pressure on the diff cases. Use the (4)3mm x 18 flat head screws provided to mount the blocks. PLEASE NOTE: These pins are designed to float. this will allow the arms and pins to rotate in bushing. lock tight the small nut, then screw the lock nut on untill it bottoms out. No need to overtighen the lock nut.