See: 6MIK

6MIK have added new aluminium clutch shoes and springs to their Optima range of products. Designed to be used with the popular Optima 4-shoe clutch, the shoes are precision machined from red anodised high-quality aluminum to provide a clutch shoe that is stable at high temperatures, offers consistent wear and increased clutch performance. The set of four clutch shoes comes with four 0.9, 1.0, and 1.1 springs so you can mix and match spring rates as needed to tune the engagement to suit your engine, track conditions and personal preferences. The Optima clutch shoes set is ideal for high horsepower engines and specially designed for high grip track conditions.