There are 3 size/dimension options for early Mustang rear leaf spring bushings. Dimensions on this kit: O.D. : 35mm Length : 31mm I.D. : 12.7mm These bushings are often overlooked when upgrading the suspension of a 4WD. Leaf spring bushings stabilize the movement of the rear axle. Inferior, worn or damaged bushings in this area will cause the solid rear axle to move and impart rear end passive steer to the vehicle. It also causes the vehicle to "wander" all over the road and be unstable under heavy braking. This can be especially noticeable carrying a load or towing a boat, RV or any significant trailer. The OE rubber bushings are designed to work at standard ride height with standard wheels and tires and with standard loads. By fitting SuperPro Bushings the rear end of your 4WD will handle just about anything you can throw at it!