The reducer is mainly composed of transmission parts (gear or worm), shaft, bearing, case and its accessories.

The cabinet is an important component of the reducer. It is the base of the transmission parts and should have sufficient strength and rigidity.

The box is usually made of grey cast iron, and a cast steel box can also be used for heavy-duty or shock-damped gear units. In order to simplify the process and reduce the cost of the reducer produced by the single unit, a steel plate welded box can be used.