RK 420MXZ Heavy-Duty Chain. These lightweight gold racing chains were developed using the same advanced alloy materials and manufacturing technology as 520MXZ4. Both 420 and 428MXZ racing chains are the lightest and strongest in their class, giving you the best value-performance rating of any motocross racing chain in the world today. Made for the serious motocross racer with all components heat-treated for high performance durability. Feature chromoly steel construction with seamless rollers and bushings, and oversized alloy pins for added strength. Max 150cc max for street or offroad use. 5,400 Lbs./ft Tensile Strength.