Carriage Bolt (DIN 603 / Round Head Square Neck)
A carriage bolt has a smooth, domed round head with a square section under the head that bites into wood or a square hole in metal, preventing the bolt from rotating during tightening. This makes it ideal for connections that can only be tightened from the nut side.
Specifications
| Standards | DIN 603, ISO 8677, ANSI B18.5 |
|---|---|
| Property Class | 4.6, 4.8, 8.8 (limited) |
| Diameter Range | M5 – M20 (1/4" – 3/4") |
| Material | Carbon steel, Stainless 304/316 |
| Surface Finish | Plain, Zinc plated, HDG, Black, Stainless |
| Common Use | Timber joinery, wood-to-metal, fence and deck construction, agricultural equipment |
Frequently Asked Questions
How does the square neck of a carriage bolt work?
The short square section directly beneath the round head pulls into the wood (or seats into a square hole) when the nut is tightened. This grip prevents the bolt from rotating, which means you can tighten the nut without holding the head with a wrench.
Can carriage bolts be used in metal?
Yes, but the metal needs a square hole that matches the neck dimension, or the assembly must rely on friction in a round hole. Most metal-to-metal carriage bolt applications use a stamped square hole in one of the parts.
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