SB12-HDR4 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. ACT's 4-pad rigid race discs are made with high quality ceramic friction materials. The chrome-moly hub is heat-treated for strength and durability. The lightweight rigid design allows for quicker shifts and smooth trouble-free service. With the 4-pad rigid race disc engagement is harsher but shifting is faster. The 4-pad rigid race disc is well-suited for the smaller disc sizes in smaller engines.