Square Nut
Nuts · square machine nut
Definition: A square nut is a four-sided nut that seats flat against a surface and resists turning in a square channel or slot.
Anatomy
■ Body■ Internal thread
Governing standards: ASME B18.2.2
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4-20 | M6 | 7/16 | 7/32 |
| 3/8-16 | M10 | 9/16 | 21/64 |
| 1/2-13 | M12 | 3/4 | 7/16 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Steel | carbon steel, zinc-plated | — | None |
| Stainless | 304 stainless | — | None |
Materials
- Zinc-plated steel
- Stainless steel
Pros & Cons
Pros
- Bigger flat bearing area than a hex nut
- Wont turn in a square channel
- Historically correct for old hardware
Cons
- Needs more room to swing a wrench
- Harder to grip with modern tools
- Rarer in stores than hex nuts
Typical Uses
- Channel and slot mounting
- Furniture
- Antique restoration
- Where a hex nut would turn
Alternatives & Related
Where to Buy
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FAQ
Square nut vs hex nut?
A square nut has four flats and resists turning in a square channel or slot; a hex nut has six flats and needs less wrench swing. Hex is the modern default.
Where are square nuts still used?
Furniture, channel mounting, unistrut-style rails, and antique hardware restoration.