Shaft Keyways and Keys: Seating, Tolerance, and Preventing Coupling Failure

The key transmits torque between a shaft and a hub. A properly seated key carries the load evenly; a poorly fitted one frets, wears, and eventually fails.

Keyway Fit

The key should seat firmly in both the shaft keyway and the hub keyway with a controlled fit. A loose key rocks under load and frets the keyway; an overly tight fit makes assembly difficult and can stress the key.

Tolerance

Keyway width and depth are held to standard tolerances so the key bears on the correct faces. The key should contact the sides of the keyway, not the bottom, so torque is transmitted through the shear faces.

Preventing Key Failure

• Use the correct key size for the shaft diameter.
• Check keyway depth and width before assembly.
• Replace worn keys and keyways rather than reusing them.

RBC Industrial stocks shaft keys, key stock, and coupling components to keep your drives transmitting torque reliably.