Carriage Bolts
Mushroom-head, square-neck bolts that lock into the hole and can't spin while you tighten the nut — for wood, sheet metal, racks, trailers and fencing.
About our carriage bolts range
A carriage bolt has a smooth, domed (mushroom) head with a square neck underneath. When tightened, the square neck bites into the material or sits in a square hole, so the bolt cannot rotate and the nut can be tightened from one side. The smooth head also leaves nothing to grip, which makes carriage bolts tamper-resistant.
We supply carriage bolts to DIN 603 / IS 5194 in mild steel, high-tensile 8.8 and stainless steel SS 304 and SS 316, with matching hex nuts and washers. They are widely used in racking and storage systems, wooden structures, trailers and truck bodies, fencing, playground equipment and conveyor guards.
Common sizes we supply: M6, M8, M10 and M12 carriage bolts — for example M8 x 50, M10 x 60 and M12 x 75 — in zinc plated and SS.
Also known in the trade as: Carriage bolt, Cup square bolt, Coach bolt, Mushroom head bolt, Square neck bolt, Round head bolt.
Available makes
Technical specifications
- Also Known As
- Cup square bolt · Coach bolt · Mushroom head square neck bolt · Round head square neck bolt
- Standard
- DIN 603 · IS 5194 · ISO 8677 · Inch: ANSI B18.5
- Material
- Mild steel · High-tensile steel · Stainless steel SS 304 / 316
- Grade
- 4.6, 8.8 · A2-70, A4-70
- Diameter
- Metric M5 – M20 · Inch 1/4" – 3/4"
- Length
- 16 mm – 300 mm
Finishes available
Zinc Plated – White / Clear
Bright silver electroplate for indoor corrosion protection.
Zinc Plated – Yellow
Yellow-passivated zinc with better salt-spray life than clear zinc.
Hot-Dip Galvanized (HDG)
Thick zinc coating for outdoor, structural, and construction use.
Black Oxide / Self Colour
Standard heat-treated finish with light oil. Default for high-tensile grades 8.8–12.9.
Stainless Steel SS 304 (A2)
Natural finish; general corrosion resistance for food, pharma, and outdoor use.
Stainless Steel SS 316 (A4)
Molybdenum grade for marine, chemical, and coastal environments.
Carriage bolt size chart (DIN 603)
| Size | Pitch (mm) | Head Dia (mm) | Head Height (mm) | Square Neck (mm) | Typical Lengths |
|---|---|---|---|---|---|
| M5 | 0.8 | 13.5 | 3.3 | 5 | 16 – 80 mm |
| M6 | 1.0 | 16.5 | 3.9 | 6 | 16 – 150 mm |
| M8 | 1.25 | 20.5 | 4.9 | 8 | 20 – 200 mm |
| M10 | 1.5 | 24.5 | 5.4 | 10 | 25 – 250 mm |
| M12 | 1.75 | 30.5 | 6.9 | 12 | 30 – 300 mm |
| M16 | 2.0 | 38.5 | 9.0 | 16 | 40 – 300 mm |
| M20 | 2.5 | 46.5 | 11.0 | 20 | 50 – 300 mm |
Dimensions are nominal. Matching DIN 934 hex nuts and DIN 125 washers available.
Common questions
What is a carriage bolt used for?
Carriage bolts join wood to wood or wood to metal, and are used in racking, trailers, fencing and playground equipment — anywhere you need a smooth, tamper-resistant head on one side.
Why does a carriage bolt have a square neck?
The square neck locks into the material or a square hole so the bolt does not turn while the nut is tightened. That means you only need a spanner on the nut side.
Do you have stainless steel carriage bolts?
Yes, in SS 304 (A2) and SS 316 (A4), suitable for outdoor, marine and food-industry use.
Hex Bolts & Nuts
Washers
Nylock Nuts
Dom Nuts