This is the 21 Tooth Optional Steel Pinion Gear for 5mm shaft CNC Steel Gear then Harden to increased wear resistance, improved fatigue life One pinion gear One set screw 4x4mm 2mm hex wrench to install the set screw Teeth count: 21 teeth Teeth pitch: 32 pitch width: 9.7mm (0.38") Inner diameter: 5.2mm (0.20") This gear is designed for 5mm or 1/8 shaft with 5mm to 1/8 conversion Sleeve