Structural Washer
Washers · F436 washer · hardened washer · ASTM F436 washer
Definition: A structural washer is a thick, hardened washer used under the head and nut of structural bolts to protect the joint surface and distribute pretension load.
Anatomy
■ Body■ Hole
Governing standards: ASTM F436
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/2 | M12 | 1-1/16 OD | 0.10 thick |
| 3/4 | M20 | 1-1/2 OD | 0.16 thick |
| 1 | M24 | 2 OD | 0.19 thick |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| F436 Type 1 | hardened carbon steel | — | F436 + manufacturer |
| F436 Type 3 | weathering steel | — | F436 Type 3 |
Materials
- Hardened carbon steel
- Weathering steel
Pros & Cons
Pros
- Hardened to resist cupping under high pretension
- Prevents the nut from gouging the steel
- Required for structural bolting
Cons
- Only used with structural bolts
- Harder and more expensive than flat washers
- Not for general hardware use
Typical Uses
- Under A325/A490 structural bolts
- Steel-to-steel connections
- Slotted and oversized holes
Alternatives & Related
- Flat Washer — General-purpose washer for non-structural work
- Fender Washer — Thin, wide washer for soft materials
Where to Buy
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FAQ
When is a structural washer required?
The RCSC specification requires F436 hardened washers under the turned element of a structural bolt, and under both head and nut in oversized or slotted holes.
Structural washer vs flat washer?
A structural washer is thicker and hardened so it does not dish or embed under high bolt pretension; a flat washer is thin and for general use.