Motors & electrical
Gearbox / speed-reducer selection basics
Reviewed August 2026
Short answer
You need the input speed, the gear ratio (or the required output speed), the output torque or the driven-machine power, the service factor for the duty, the gearbox type and mounting (foot, flange, shaft-mounted), and the input and output shaft dimensions. The service factor is the field most often missed — it accounts for shock loading and running hours.
A gearbox is specified from the load, not from the old label alone — though the label is the fastest starting point.
What defines the gearbox
- Input speed — usually the motor speed (r/min)
- Ratio — or the required output speed
- Output torque — or the driven-machine power, so torque can be calculated
- Service factor — for the duty (conveyor, crusher, mixer, fan) and the running hours
- Type and mounting — helical, bevel-helical, worm; foot, flange or shaft-mounted
- Shaft dimensions — input and output shaft diameters, lengths and keyways; hollow-bore size for a shaft-mount
Shaft-mounted reducers
Common on conveyor drives. Add the torque-arm arrangement, the driven-shaft diameter, and whether a backstop (anti-runback) is required — inclined conveyors usually need one.
What to send us
A photo of the gearbox nameplate, the motor details, the driven machine and its duty, and the mounting and shaft dimensions. We confirm the ratio, rating and fit.
