Torque arms and driveshafts are both used to transmit torque from one point to another, but they do so in different ways. A torque arm is a rigid member that is attached to the frame of a vehicle and to the rear axle. It allows the rear axle to move up and down relative to the frame, but it prevents the axle from rotating. A driveshaft, on the other hand, is a rotating shaft that is connected to the transmission and to the rear axle. It transmits torque from the transmission to the axle, allowing the wheels to turn.

Torque arms are typically used in applications where there is a high amount of torque being transmitted, such as in high-performance vehicles. They are also used in applications where it is important to prevent the rear axle from rotating, such as in off-road vehicles.

There are a few factors to consider when choosing a torque arm, including the amount of torque that will be transmitted, the length of the torque arm, and the material that the torque arm is made from. It is important to choose a torque arm that is rated for the amount of torque that will be transmitted, and that is long enough to provide adequate leverage.

Steel is a strong and durable metal that is well-suited for use in torque arms. It is also relatively lightweight, which makes it a versatile option. However, steel is not as light as some other materials, such as aluminum, so it may not be the best choice for applications where weight is a concern.