Carriage Bolts
Round heads with a square neck that locks against turning.
Domed heads and square necks for timber and slotted-steel connections, plain or galvanized.
Specifications & technical data.
Carriage bolts to ASME B18.5 — the round head and square neck lock the bolt against turning so the joint tightens from the nut side alone.
Download our carriage bolt dimensioning table (PDF)
| Nominal Size or Basic Bolt Diameter | E | A | H | O | P | Q | R | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Body Diameter | Head Diameter | Head Height | Square Width | Square Depth | Max. Corner Radius on Square | Max. Fillet Radius | |||||||
| Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | ||||
| #10 | 0.1900 | 0.199 | 0.159 | 0.469 | 0.436 | 0.114 | 0.094 | 0.199 | 0.185 | 0.125 | 0.094 | 0.031 | 0.031 |
| 1/4" | 0.2500 | 0.260 | 0.213 | 0.594 | 0.563 | 0.145 | 0.125 | 0.260 | 0.245 | 0.156 | 0.125 | 0.031 | 0.031 |
| 5/16" | 0.3125 | 0.324 | 0.272 | 0.719 | 0.688 | 0.176 | 0.156 | 0.324 | 0.307 | 0.187 | 0.156 | 0.031 | 0.031 |
| 3/8" | 0.3750 | 0.388 | 0.329 | 0.844 | 0.782 | 0.208 | 0.188 | 0.388 | 0.368 | 0.219 | 0.188 | 0.047 | 0.031 |
| 7/16" | 0.4375 | 0.452 | 0.385 | 0.969 | 0.907 | 0.239 | 0.219 | 0.452 | 0.431 | 0.250 | 0.219 | 0.047 | 0.031 |
| 1/2" | 0.5000 | 0.515 | 0.444 | 1.094 | 1.032 | 0.270 | 0.250 | 0.515 | 0.492 | 0.281 | 0.250 | 0.047 | 0.031 |
| 5/8" | 0.6250 | 0.642 | 0.559 | 1.344 | 1.219 | 0.344 | 0.313 | 0.642 | 0.616 | 0.344 | 0.313 | 0.078 | 0.062 |
| 3/4" | 0.7500 | 0.768 | 0.678 | 1.594 | 1.469 | 0.406 | 0.375 | 0.768 | 0.741 | 0.406 | 0.375 | 0.078 | 0.062 |
| 7/8" | 0.8750 | 0.895 | 0.795 | 1.844 | 1.719 | 0.469 | 0.438 | 0.895 | 0.865 | 0.469 | 0.438 | 0.094 | 0.062 |
| 1" | 1.0000 | 1.022 | 0.910 | 2.094 | 1.969 | 0.531 | 0.500 | 1.022 | 0.990 | 0.531 | 0.500 | 0.094 | 0.062 |
All dimensions in inches, per ASME B18.5-2012. Confirm requirements with our estimating team.
Standards.
What are carriage bolts?
A carriage bolt has a smooth domed head with a square neck directly beneath it. Drawn into a square hole or soft material, the neck stops the bolt spinning — so the whole joint is made up from the nut side, and the finished face shows only a clean button of steel.
- Round head — no external drive
- Square neck resists rotation
- Tightened entirely from the nut side
- Plain, zinc, galvanized and stainless
Other names
- Round head square neck bolts
- Coach bolts
- Cup head bolts
Tips for purchasing
- Match the square to the hole — O and P in the table set the anti-rotation fit.
- Timber and galvanized service is the classic use — order hot-dip with oversize nuts.
- Head style variations (fin neck, ribbed neck) available to order.
- Certs and traceability available on request.
Materials.
Representative capabilities — every item is manufactured or certified to your specification. Confirm requirements with our estimating team.
