Fenner HTD timing belts are the first generation of metric curvilinear tooth form synchronous belts for high torque drives. HTD-profile timing belt · 3M - 5M: applications in light electrical appliance power transmissions - electric tools - industrial applications. 5 mm Pitch HTD Timing Belts with Kevlar Reinforced Cords. SIT TOP DRIVE® HTD belt is an evolution of standard positive drive belts. HTD Polyurethane Timing Belts with steel tension members come in 3, 5, 8 & 14mm. HTD® belts provide thirty percent increase in horsepower ratings, as compared to traditional timing belts.