Moog CK621201 Control Arm and Ball Joint Assembly Moog engineered steel composition results in a stronger component Problem Solver patented cover plate design allows for tighter tolerances vs traditional cover plate designs, providing a more durable and extended life part. Exclusive cover plate protects against contaminants leaking into the bearing surface. Greaseable socket design allows new lubricant to flush contaminants from the assembly, reducing corrosion and wear Loose or worn chassis parts can lead to premature tire wear