Timber Bolt
Bolts · mushroom head bolt · dome head bolt · timber dome bolt
Definition: A timber bolt has a large low-dome (mushroom) head and a square or ribbed neck, made for heavy timber connections like docks, bridges, and retaining walls.
Anatomy & Schematic
■ Head■ Shank■ Threads■ Point
Governing standards: Manufacturer specified (no universal standard)
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 3/8-16 | M10 | 1-1/4 | 4 to 10 long |
| 1/2-13 | M12 | 1-1/2 | 5 to 14 long |
| 3/4-10 | M20 | 2 | 6 to 18 long |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Grade 2 | low carbon steel | 74,000 | None |
| Hot-dip galvanized | steel | — | For outdoor timber |
Materials
- Zinc-plated steel
- Hot-dip galvanized steel
- Stainless steel
Pros & Cons
Pros
- Large head spreads load on wood
- Square neck resists spin
- Galvanized for outdoor life
Cons
- Heavy
- Needs large pre-drilled holes
- Specialty supply
Typical Uses
- Timber bridges and boardwalks
- Docks and piers
- Retaining walls
- Pole barns
Alternatives & Related
- Carriage Bolt — Smaller dome head for general wood
- Lag Bolt — Drives directly into wood without a nut
Where to Buy
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FAQ
What is a timber bolt used for?
Heavy timber connections — docks, bridges, boardwalks, and retaining walls — where a big head spreads load and a square neck stops rotation.
Timber bolt vs carriage bolt?
Timber bolts are larger with a broad mushroom head for heavy timbers; carriage bolts are smaller general-purpose wood bolts.