齿轮

(machine) gear / pinion (gear wheel)

tooth / CL:顆|颗[ke1]

wheel / disk / ring / steamship / to take turns / to rotate / by turn / classifier for big round objects: disk, or recurring events: round, turn

wheel; disk; ring / steamship / to take turns; to rotate / classifier for big round objects: disk, or recurring events: round, turn

rack and pinion

differential gear

gearbox

gear drive

pinion gear