Which of the following is NOT a main component of a manual transmission?

A manual transmission primarily consists of several key components that work together to transmit power from the engine to the wheels while allowing the driver to control the vehicle's speed and torque. The gearbox is crucial as it contains the gears that determine the vehicle's speed and the torque supplied to the wheels. The clutch is another essential component that engages and disengages the engine from the transmission, allowing the driver to change gears. The gear lever, or shifter, is the interface through which the driver selects different gears.

In this context, a fuel injector is unrelated to the manual transmission system. Fuel injectors are part of the engine's fuel delivery system, responsible for injecting fuel into the combustion chamber for efficient combustion. Since fuel injectors do not play any role in the mechanics of gear shifting or power transmission in a manual transmission, it is recognized as the component that does not belong in the context of this question.