Developed to produce a quick upshift and improved backshift for excellent throttle response. Dual-angle-option helix offers fine-tunin for changing conditions. Available in a variety of multi-angles for almost any application. ER helixes are for fits Ski-Doo and fits POL machines with engine revers. Type F equals full progressive; type .46 equals .46 progressive. Helixes for TIED8 and TSS-04 clutches are NOT interchangeable. Sold each.