Ball joints are spherical bearings that connect the control arms to the steering knuckles. Ball joints are the critical component of the front suspension that connect various links and allow them to move. A ball joint consists of a bearing stud and socket enclosed in a casing; all these parts are made of steel. The bearing stud is tapered and threaded, and fits into a tapered hole in the steering knuckle.A protective encasing prevents dirt from getting into the joint assembly. Usually, this is a rubber-like boot that allows movement and expansion of lubricant. Symptoms for worn out ball joints include steering vibration, loosened steering etc.