KEVOS® MAKEOS · Fasteners
Set-Screw Hub Retention (Torque, Axial Hold, Screws Needed)
Will set screws hold this hub on its shaft for the power and axial load, how many are needed, and when should I use a key instead?
Check of a hub, collar or pulley held by cup-point set screws: power, torque and holding force per screw by the handbook empirical rule (as the set-screw holding tool), the torque needed with your safety factor, the number of screws needed, the torque and axial capacity of the screws you fit, and the advice to change to a key or clamp collar when more than two screws would be needed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Shaft diameter | mm | Diameter of the shaft. |
| Set-screw diameter | mm | Nominal diameter of the set screws. |
| Shaft speed | rpm | Speed of the shaft. |
| Power transmitted | kW | Power passing through the hub. |
| Safety factor | Safety factor on the holding torque and axial force (higher for shock and reversing loads). | |
| Set screws fitted | Number of set screws fitted (usually one or two, about 90° apart). | |
| Axial load on the hub | N | Axial force trying to slide the hub along the shaft. |
Method and formulas
- Handbook rule (inch units): holding power hp = D N d^2.3 ÷ 50; torque = 1250 D d^2.3 lb·in, converted to metric (as the set-screw holding tool).
- Torque needed = P ÷ ω × SF; screws needed = torque needed ÷ torque per screw (rounded up).
- Axial capacity ≈ holding force per screw × screws fitted, against axial load × SF.
- Example: each M12.7 screw holds 28.679 N·m; 2 screws give 57.358 N·m against 32.043 N·m needed.
Limitations
- Empirical rule for cup-point screws on a hardened screw and unhardened shaft; flats or spot drills change the hold.
- Vibration loosens set screws: use thread locker or a key for critical drives.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a set-screw hub for a motor or pulley
- Decide between set screws and a key
- Check axial hold of a collar
Who it is for
- Design engineers
- Maintenance engineers
- Machine designers
What you get
- Holding per screw (power, torque, force)
- Screws needed and capacity of those fitted
- Torque and axial checks
Interpreting the result
- Two screws at 90° hold better than two at 180°, and a flat on the shaft stops marking.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1699–1700. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Set-Screw Hub Retention (Torque, Axial Hold, Screws Needed) calculator
