Hobbypower HSP 39T 44T Throttle Gear Upgrade Steel Diff. Gear 02040 02041 for 94122 94102 HSP Upgrade Steel Diff. Gear set( 39T & 44T) for 1/10 HSP 94122 94102 Nitro car Use this steel gear to replace the stock plastic gear, upgrade you car. the steel gear will be more durable, and effectively avoid jamming gear when racing. Install suggestion: take off the speed transmission kit direct, and replace the gear, do not take off the engine.