Gear is a mechanical element with gears on the rim to continuously mesh and transmit motion and power. The application of gears in transmission appeared very early. At the end of the 19th century, the principle of generating gear cutting method and the emergence of special machine tools and cutting tools using this principle.

Belt pulley is a kind of hub part, which is generally relatively large in size. The manufacturing process is generally dominated by casting and forging.

The handle is an input device of a video game machine. By manipulating its buttons, it can control the simulated characters on the computer. The handle has two words in English: gamepad and joystick. The difference is that the gamepad is held by hand and joystick is placed flat on the table (like an arcade, it is mainly used for arcade simulator and flight games)

The piston is connected with the crankshaft, and the force on the piston is transmitted to the crankshaft to convert the reciprocating motion of the piston into the rotary motion of the crankshaft.