A set screw is used along with a key to hold the hub axially, and to minimize rotational backlash when the shaft rotates in both directions. Diameter selections of set screws for use over keys are given in ANSI B17.1-1967 standard. These selections are given in this page and can be used as a guide but their use shall be dependent upon design considerations.
Key: A demountable machinery part which, when assembled into keyseats, provides a positive means for transmitting torque between the shaft and hub.
Keyseat: An axially located rectangular groove in a shaft or hub.