There are 3 basic types of ball joints that are used in suspension systems: 

Press in — a press in ball joint design works on the principle of friction, or interference. The ball joint is larger than the hole inside the control arm or knuckle. When the ball joint is pressed into the control arm, a high amount of friction is generated that holds the ball joint tightly in place. 

Bolt In — a bolt in ball joint uses a mounting flange that bolts on to the control arm using 3 or more bolts and nuts. Many of the OEM ball joints on this application will come riveted only on the original vehicle. As they wear and need to be replaced, the rivets are removed, and the ball joint is replaced with an aftermarket bolt in design. 

Unitized — a unitized ball joint application replaces the individual ball joint. This design completely integrates the ball joint pivot into the design and construction of the control arm assembly, forming one solid container arm. This design has become very popular with the use of aluminum design control arms. Replacement of unitized ball joints requires the entire control arm assembly to be replaced.