Zinc Gear Box Case

Zinc gearbox 

transmission  is a  machine  in a  power  transmission system, which provides controlled application of the power. Often the term transmission refers simply to the  gearbox  that uses  gears  and  gear trains  to provide  speed  and  torque  conversions from a rotating power source to another device. 

In  British English , the term  transmission  refers to the whole  drivetrain , including  clutch , gearbox, prop shaft (for rear-wheel drive),  differential , and final drive shafts. In  American  English, however, the term refers more specifically to the gearbox alone , and detailed usage differs.