Zinc Blue M12 1045 Gr.8.8 METAL BOLT Carriage Bolt Large Round Head DIN603

Zinc Blue M12 1045 Gr.8.8 METAL BOLT Carriage Bolt Large Round Head DIN603

Product Description

Carriage Bolt is produced from round wire or hot-rolled rod in a multi-station cold- or hot-forging process. A shallow, large-diameter dome head is formed first; immediately after, a square or short ribbed neck is extruded just under the head. The square section is slightly wider than the thread root diameter, so it bites into the wood or into a square punched hole when the bolt is driven in. After head and neck forming, the blank is thread-rolled between flat dies to generate a Class 6g (metric) or 2A (inch) thread with a smooth, work-hardened surface that gives 25-30 % higher fatigue strength than cut threads. Heat-treatment follows when mechanical properties above 400 MPa are required: medium-carbon grades are quenched and tempered at 550 °C to achieve Grade 8.8 or A307-C strength, while stainless steels are solution-annealed at 1050 °C and water-quenched to restore corrosion resistance. Final finishing is selected for the target environment: zinc electroplating (5–8 µm) or hot-dip galvanizing (45–60 µm) for carbon steel outdoor use, black oxide plus oil for indoor furniture, Dacromet or Geomet for 1000-hour salt-spray demand, and passivation or electropolishing for stainless A2-70/A4-80 bolts used in food equipment. The entire process is governed by DIN 603, ISO 8678, ASME B18.5 and EN 14399-7 dimensional standards, so every Carriage Bolt delivers consistent head height, square width across flats, and thread fit for automatic assembly lines.

Secures wooden sleepers to steel bridge beams; the large head distributes clamp force, preventing timber crushing under 40-ton loads.

Key Features

Yellow finish signals high-strength grade to site inspectors; square neck stops spin-out when vibrating pneumatic wrenches are used upside-down.