Robinson Racing 2028 Hard Steel Motor Pinion 5mm Bore / 48P / 28T is a high-quality gear that is perfect for use with toy trains and train sets. This gear is constructed of hardened machined steel, making it durable and long-lasting. It features 28 teeth and a pitch of 48, with a bore size of 5mm that is compatible with Traxxas, Associated, and HPI models. The gear comes with a 4mm set screw and requires a 2mm hex wrench, GPMR8011. With its high-quality construction and precise specifications, Robinson Racing 2028 Hard Steel Motor Pinion 5mm Bore / 48P / 28T is the perfect choice for any toy train or train set enthusiast.