The casters have a hollow center of the wheel and are designed to be a shape that does not collect dust, etc. Screw T: M10. Thread Pitch: 0.06 inches (1.5 mm). Load Capacity: 1.5 inches (39.2 mm). Load Capacity: 1.6 lbs (40 kg). Shaft Length: 6.0 inches (15 mm). Wheel Diameter: D 2.6 inches (65 mm). Wheel Width: 1 mm). Mounting Height: 1 mm). Metal Fittings: Steel; Wheels. : Nylon + Polyurethane