A machined slot or groove along the axis of a shaft or inside a hub. It holds a small block of metal called a key, locking the two parts together to transmit torque without slipping. The depth and width must be cut to tight tolerances to prevent the key from rolling or shearing under heavy loads.
Heard on the job
Check the keyway on that pump shaft for wallowed out edges before we press the new impeller on.
Insider tip
A damaged keyway often means the entire shaft must be replaced or welded and re-machined, as a loose fit will quickly destroy the new key.