This is a replacement T-Lock Electronic Differential Controller, intended for use with the Traxxas Summit Monster Truck. The T-Lock Electronic Differential Controller gives you the ability to lock the differentials and shift from low to high gear right from the transmitter. No need to break from the action to swap gears or install locking parts. Tear up the trail in "high range" with a 25:1 ratio for dirt-slinging speed. When the terrain turns technical, drop it into "low range" for a 70:1 ratio and unreal climbing torque. For the ultimate in climbing traction, flip the T-Lock switch to lock the front differential. Need even more grip? Activate the rear T-Lock diff for fully-loaded 4WD power no matter which tire is gripping or slipping.