GT2 Aluminium Timing Pulley 20 Teeth M4 Screw 5M Belt For RepRap 3D Printer Prusa CNCSpecification:GT2 Pulley:Material: AluminiumNumber of teeth: 20Tooth pitch: 2mmDiameter of bore: 5mmFlange: DoubleTooth width: 7mm (to fit 6mm timing belt)Grub screws: M4GT2 Belt:Tooth pitch: 2mmWidth: 6mmBelt shape: Open endMaterial: Fibre-reinforced rubberLength: 5MFeatures:T2 timing belts and compatible pulleys (GT2 pulley) are popular choices for RepRaps and RepStraps.The GT2 series of belts are designed specifically for linear motion. They use a rounded tooth profile that guarantees that the belt tooth fits smoothly and accurately in the pulley groove, so when you reverse the pulley direction, there is no room for the belt to move in the groove.For best performance you want at least 6 teeth in contact with the pulley at any given time. That minimizes the chance of the belt slipping, and helps reduce backlash even further. In practice that means you want a minimum of a 12 tooth pulleyPackage includes:1 x GT2 Belt  4 x GT2 Pulley8 x Screws1 x Wrench (As Pictures)