Traditionally the tail rotor of a model helicopter was powered by a belt, called a Gilmer belt. The Gilmer belt is flexible belt with embedded teeth designed to work with notched or sprocketed gear. The Gilmer belt is used in a wide variety of applications where high power transmission is required. Since they use toothed belts they rarely slip, but do create some drag on the engine.
Align T-Rex model helicopters use a Torque tube to power the tail rotors. A torque tube is a type of driveshaft that uses beveled gears instead of notched guide wheels. They are more durable and create less drag on the motor. However anything that stops the tail rotor from spinning, like a boom strike or a crash could cause the drive gears to strip. This part can be used to replace a damaged Torque Tube in your model helicopter.