ACT 4-Puck Rigid Race Disc Subaru Impreza WRX STI (4240018) is a race disc made with high quality, ceramic friction materials. The disc engagement is harsher, but shifting is faster. The race disc features top grade rivets to securely fasten the part together. The rivet design and materials are carefully selected for maximum strength. The 4-pad rigid race disc is well-suited for the smaller disc sizes in smaller engines.