Carriage Bolts

Square-neck coach bolts for timber, metal and general construction — manufactured to DIN, ISO, ASME and GB standards.

What Are Carriage Bolts?

A carriage bolt — also called a coach bolt — has a domed or countersunk head with a square neck directly beneath it. The square neck bites into the mating material and stops the bolt from rotating while the nut is tightened, which makes it the preferred fastener for wood-to-wood, wood-to-metal and metal-to-metal joints where access to the head side is limited.

Typical applications include timber framing, furniture assembly, fencing, agricultural equipment, trailers, playground structures and light steel construction. Carriage bolts are available in carbon steel, stainless steel and brass, with zinc, hot-dip galvanized, black oxide and other surface finishes.

Specifications

ProcessCold heading, thread rollingMaterialCarbon steel (4.8/8.8), stainless steel (A2-70/A4-80), brassStandardsDIN 603, ISO 8677, ASME B18.5, GB/T 14Size RangeM6 – M24, 16mm – 300mm lengthSurface TreatmentZinc plated, hot-dip galvanized, black oxide, plain, DacrometOEM / ODMAvailable (custom head, length, plating)Lead TimeSamples: 5–7 days; Mass production: 15–25 daysInspectionFAI, dimensional check, hardness test, salt spray testPackagingPoly bags, cartons, pallets or custom export packing

Common Carriage Bolt Types

Carbon Steel Carriage Bolt

Grade 4.8 / 8.8, zinc plated or hot-dip galvanized. The most economical choice for general construction and woodworking.

Brass Round Head Bolt

Corrosion resistant and decorative. Ideal for marine, electrical and furniture applications where appearance matters.

Standards & Compliance

Carriage bolts are manufactured to internationally recognized standards. Tell us your target standard or country of use, and we will match the specification exactly.

DIN 603

Coach bolt with round head and square neck

View Standard

ISO 8677

Carriage bolts — product grades A and B

View Standard

ASME B18.5

Round head square neck bolts

View Standard

GB/T 14

Carriage bolts (square neck), full and partial thread

View Standard

Carriage Bolt Manufacturing Process

1. Wire drawing — raw material (carbon steel, alloy steel) is cold-drawn to the required diameter.
2. Cold heading — the wire is formed into the round head and square neck in a single stroke.
3. Thread rolling — threads are rolled or cut to the required pitch and length.
4. Heat treatment — improves mechanical properties for grade 8.8 and above.
5. Surface treatment — zinc plating, galvanizing or black oxide for corrosion resistance.
6. Inspection & packing — dimensional, hardness and salt-spray checks before export packing.

Quality Inspection

Inspection Reports

Dimensional reports, material certificates and plating test results are available for every batch.

First Article Inspection (FAI)

FAI verifies critical dimensions before mass production, reducing rework risk and protecting your schedule.

Third-Party Inspection

SGS, BV, TÜV or other third-party inspection can be arranged at the factory before shipment on your request.

Frequently Asked Questions

What is the difference between a carriage bolt and a hex bolt? A carriage bolt has a dome head and square neck that prevent rotation; a hex bolt has a hexagonal head driven by a wrench. Carriage bolts are designed for applications where only one side is accessible.
What is the minimum order quantity (MOQ)? Standard sizes: 5,000 pcs. Trial orders from 500 pcs are welcome for testing.
Do you provide free samples? Yes, samples are free for standard carriage bolts — you pay only the shipping cost.
Can you make custom sizes? Yes, we support OEM/ODM for custom diameters, lengths, materials and surface finishes.
What is the typical lead time? Samples: 5–7 days. Mass production: 15–25 days depending on quantity and finish.