ZM4-HDG6 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 6-pad, spring-centered race disc features a spring-center to properly damp torsional vibrations and resist failure under harsh conditions. ACT spring retainers utilize wraparound spring windows and thicker retainer stampings to provide spring support, reduce stress concentrations, and increase strength and reliability. With the 6-pad, spring-centered race disc, engagement is harsher, but shifting is faster. The 6-pad, spring-centered disc is recommended for larger clutch sizes to absorb more heat.