Material: Aluminium similar to EN AW2017A. Flanges zinc-plated steel. Screw DIN 912-12.9, black.The hubs of the pulleys are slotted, similar to single-split clamp collars (shaft collars). The pulleys are fixed on the shafts with the clamping screw. No more machining, quick assembly, does not damage the shaft, even distribution of clamping forces.Bore BH7: Bore tolerance in wheel area H7 continuous, in clamping area H7 before slotting. R: Interference circle-Ø screw head. Transmittable torque: Max. Friction torque of the hub.