UMI's rear weight jacks provide ride height adjustment and excellent handling for your 3rd or 4th Gen GM F-Body. The kit includes custom wound premium race quality springs and our own unique spring perches featuring a smooth acting Torrington bearing. The heavy duty jack screw and spring pad is easily adjusted by using a 3/4" socket, extension and ratchet through the bottom of the existing hole in the axle. Installation requires simply removing the standard spring and inserting the weight jack assembly. Minor grinding required on left axle pad – instructions included. 100% Made In USA.