This is a Protek 48P Light Weight Aluminum Pinion Gear. These are light-weight, hard anodized, CNC machined aluminum off road pinion gears that allow your motor to spool up quicker and improve acceleration when powering out of the corners.
Machined from 7075-T6 aluminum and hard anodized, these precision cut gears are durable and ideal for any 48-pitch application. Plus, the 18 tooth and larger gears have been machined on the back side to remove as much weight as possible, without sacrificing strength. Each gear includes a setscrew to make installation easy.