Set Screw Holding Power & Tightening Torque
Set screws hold collars, pulleys, gears, and knobs on shafts. Their holding power depends on the point style, material hardness, and seating torque. Under-torqued set screws are the most common cause of components slipping on shafts.
Recommended Tightening Torque
| Set Screw Size | Cup Point Torque (in-lbs) | Axial Holding Force (lbs) | Torsional Holding (in-lbs) |
|---|---|---|---|
| #4-40 | 5.2 | 50 | 3 |
| #5-40 | 7.7 | 75 | 5 |
| #6-32 | 10 | 100 | 8 |
| #8-32 | 20 | 150 | 13 |
| #10-24 | 36 | 200 | 20 |
| 1/4-20 | 87 | 400 | 50 |
| 5/16-18 | 165 | 700 | 110 |
| 3/8-16 | 290 | 1,000 | 190 |
| 1/2-13 | 620 | 1,500 | 375 |
| 5/8-11 | 1,325 | 2,000 | 625 |
| 3/4-10 | 2,400 | 2,500 | 940 |
Values are for alloy steel (180 ksi) cup point set screws on a medium carbon steel shaft. Holding forces are approximate and vary with surface finish and hardness.
Point Styles — When to Use Each
| Point Style | Holding Power | Best For | Shaft Damage |
|---|---|---|---|
| Cup Point | Highest | General purpose, permanent installation | Creates a divot (intentional — it’s how it grips) |
| Cone Point | Very High | Permanent mounting into a drilled dimple | Requires pre-drilled hole in shaft |
| Flat Point | Lowest | Frequent adjustment, soft shafts, no damage allowed | Minimal |
| Oval Point | Low-Medium | Adjustment against hardened surfaces | Minimal (rounded contact) |
| Knurled Cup | Highest | Vibration environments, permanent | Aggressive — chews into shaft |
| Dog Point | N/A (locating) | Locating, indexing — pilot fits into a hole | None (doesn’t contact shaft surface) |
Improving Set Screw Holding Power
- Use a shaft flat. A flat spot milled on the shaft gives the set screw a square surface to push against — dramatically increases both axial and torsional holding.
- Use two set screws at 90°. Standard practice for collars and couplings. The second screw prevents the first from loosening.
- Match hardness. The set screw should be harder than the shaft. Alloy steel set screws (Rc 45-50) on mild steel shafts work well. Stainless set screws on stainless shafts will gall.
- Use thread locker. Loctite 242 (blue, removable) prevents loosening from vibration without making disassembly impossible.
- Upgrade to a clamping collar when set screws aren’t enough. Clamping collars distribute force around the shaft instead of point-loading.
Related: Socket Head Cap Screw Dimensions | Bolt Torque Chart | Bolt Grade ID