BM4-HDSD kit features ACT’s most popular Heavy Duty pressure plate. ACT Heavy Duty pressure plates use exclusive diaphragm design to increase clamp load, reduce deflection and maximize clutch life. All diaphragms endure a four-stage, heat-treating process for unparalleled performance. ACT pressure plates have precision cover stampings to provide rigidity and consistency. The ACT performance street rigid-hub discs feature premium organic materials with high copper content for better heat transfer and steel-backed lining for greater burst strength and durability. The chrome-moly hub is heat-treated for strength and durability. Rivet design and materials are carefully selected for maximum strength. These discs are the minimum weight street disc for faster shifts. ACT?s street rigid-hub discs provide race-proven performance with street manageability.