This is the 18 Tooth 48 Pitch Pinion Gear for the HPI RS4 Car Kits. This Gear installs on the motor shaft and meshes with the Spur Gear to power the vehicle. FEATURES: Constructed of steel. Replaces worn or damaged pinion gears. YOU WILL RECEIVE: One 18 Tooth 48 Pitch Pinion Gear for the HPI RS4 Car Kits with Set Screw. 48 pitch gear ratio chart REQUIREMENTS: Installing on motor shaft and tightening set screw with a 1.5mm wrench, can use HPIR1491. SPECIFICATIONS: Diameter of center hole: 1/8" (3mm) Number of Teeth: 18 Pitch: 48 cmc 03/07/02 ir/kh &