Square Plate Washer
Washers · timber washer · dock washer · square washer
Definition: A square plate washer is a large, thick square washer that spreads heavy bolt load over soft wood — used on timber, docks, and structural connections.
Anatomy
■ Body■ Hole
Governing standards: ASTM F436 · Manufacturer specified
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| for 1/2 | M12 | 2 x 2 | 1/4 |
| for 5/8 | M16 | 2-1/2 x 2-1/2 | 5/16 |
| for 3/4 | M20 | 3 x 3 | 3/8 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Hot-dip galvanized | steel | — | None |
| Stainless / plain | varies | — | None |
Materials
- Hot-dip galvanized steel
- Stainless steel
- Plain steel
Pros & Cons
Pros
- Large bearing area protects wood
- Resists pull-through
- Galvanized for outdoor timber
Cons
- Heavy
- Visible and utilitarian looking
- Overkill for general bolting
Typical Uses
- Timber connections
- Docks and piers
- Ledgers and beams
- Pole barns
Alternatives & Related
- Structural Washer — Hardened round washer for steel-to-steel
- Fender Washer — Lighter round washer for thin materials
Where to Buy
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FAQ
What is a square plate washer used for?
Spreading bolt load over soft wood in timber and dock construction, so the head or nut does not crush or pull through the wood.
Square vs round plate washer?
Square plates resist rotation and cover more area in corners; round plates are the general structural choice. Both spread load over soft materials.