Set Screw
Screws · grub screw · headless screw
Definition: A set screw is a headless screw driven with a hex key that locks a collar, pulley, or knob onto a shaft by pressing its point against the shaft.
Anatomy & Schematic
■ Head■ Shank■ Threads■ Point
Governing standards: ASME B18.3
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| #6-32 | M4 x 0.7 | — | 1/8–1 |
| #10-24 | M5 x 0.8 | — | 1/8–1-1/4 |
| 1/4-20 | M6 x 1.0 | — | 1/4–2 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Alloy steel | alloy steel, heat-treated | 180,000 | Black oxide / zinc |
| 18-8 stainless | 304 stainless | 70,000 | None |
Materials
- Alloy steel (black oxide)
- Stainless steel 18-8
- Brass
Pros & Cons
Pros
- Sits completely flush — nothing protrudes
- Cheap and compact
- Point styles for different grip needs
Cons
- Low torque capacity — not for heavy loads
- Cup point dimples/marrs the shaft
- Easy to overtighten and strip
Typical Uses
- Locking pulleys and gears to shafts
- Retaining knobs and handles
- Collars and shaft accessories
Alternatives & Related
- Socket Head Cap Screw — A headed screw for clamping, not just locking
- Shoulder Bolt — Where the shaft needs a precision bearing surface
Where to Buy
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FAQ
What is a set screw used for?
It locks a rotating part — a pulley, gear, collar, or knob — onto a shaft by driving its point into the shaft surface.
Cup point vs cone point set screw?
A cup point is the general-purpose default; a cone point bites deeper for permanent positioning; a flat point protects a shaft you must not mar; a dog point fits a pre-drilled hole.