Different spindle adapters are needed to attach the upper ball joints to the different types of spindle configurations that can exist on the Fox platformed Mustang (from 1979 to 2000). Even Ford's FR 500 concept Mustang uses a spindle adapter to connect the spindle to the upper ball joint of its radical suspension. The set on the right are Fox-3 types, and the other set are SN95 types, neither of which worked on my car.