Acorn Nut
Nuts · cap nut · dome nut · crown nut
Definition: An acorn nut is a hex nut with a closed, domed top that covers the exposed thread end, protecting it and giving a finished appearance.
Anatomy
■ Body■ Internal thread
Governing standards: ASME B18.2.2 · DIN 1587
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4-20 | M6 | 7/16 | 7/16 |
| 3/8-16 | M10 | 9/16 | 5/8 |
| 1/2-13 | M12 | 3/4 | 13/16 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Zinc steel | carbon steel, zinc-plated | — | None |
| Stainless / brass | 304 stainless or brass | — | None |
Materials
- Zinc-plated steel
- Stainless steel
- Brass
- Chrome-plated
Pros & Cons
Pros
- Covers sharp thread ends safely
- Clean, finished look
- Protects threads from corrosion and damage
Cons
- Thread depth is limited by the dome
- Cannot use on a stud that must extend through
- Pricier than a plain hex nut
Typical Uses
- Handrails and exposed bolting
- Furniture and fixtures
- Playground equipment
- Anything with sharp exposed threads
Alternatives & Related
- Hex Nut — Standard nut where the thread end is acceptable
- Coupling Nut — Long nut for joining rod ends
Where to Buy
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FAQ
Acorn nut vs cap nut?
They are the same thing — a domed, closed-end hex nut. High-crown and low-crown styles vary the dome height.
Can an acorn nut thread all the way on?
Only until the bolt end touches the inside of the dome, so the bolt must not be longer than the nut allows.