SDE Pulleys, or Single Disc Pulleys, are a one-piece, steel, pulley with a continuous weld of the disc to the rim, heavy-duty construction, and a high compression hub and bushing. SDE Pulleys are capable of reducing stress and deflection due to the nature of their construction. Single Disc Pulleys are available with other hub and bushing systems, please reference the Bushing Insets Chart on page five of the PPI Precision Pulley Brochure to make sure you select the right size.