From the factory, suspension arms typically use rubber bushings at the hinge point and studded, greased ball joints of some type at the spindle end. The rubber provides some flex to prevent suspension harshness and helps isolate noise transmission into the chassis. Aftermarket replacement arms such as the one shown at top typically use urethane bushings in place of rubber, and use spherical uniballs. The urethane provides more precise and firm suspension control. The uniball provides greater strength than the OEM ball joint and can be mounted in double-shear with a bolt that can hold the joint captive even if it wears and breaks.