The gearbox is the first mechanical component in the driveline, entrusted with the task of modifying the torque characteristic of an engine by directly controlling the gears while driving.
The gearbox contains  the following mechanical structures within it: the input shaft, the main shaft and the countershaft. On these three components there are sprockets of different sizes, which correspond to the different gears, or torque converter.

Of the various components involved in the mechanical transmission, the gear lever is one of the most important and, together with the clutch, allows the transmission ratio between the engine and the wheels to be altered while maintaining the rotation speed of the former at an optimum level.