Product Introduction
Metric carriage bolts manufactured to DIN 603, product grade C. The fastener combines a round (mushroom) head, a square neck directly beneath the head, and a partial thread configuration. Thread sizes M5 to M20 in metric coarse pitch per ISO 261. The square neck engages a punched or broached square hole to provide positive anti-rotation locking while the nut is tightened from the opposite side. Material options include carbon steel property classes 4.6, 4.8, 8.8, and 10.9, plus stainless steel A2-70 and A4-80. Surface finishes: zinc plating, hot-dip galvanizing (HDG), black oxide, or Dacromet.

Material & Mechanical Properties
Carbon steel grades conform to ISO 898-1: class 4.6 (tensile 400 MPa, yield 240 MPa, low-carbon steel C1008–C1022); class 8.8 (tensile 800 MPa, yield 640 MPa, quenched and tempered medium-carbon or boron steel). Stainless grades to ISO 3506-1: A2-70 (tensile 700 MPa), A4-80 (tensile 800 MPa) for improved pitting resistance in chloride environments. Mechanical values are certified by lot with full traceability.

Geometry & Thread
DIN 603 half-thread geometry: thread length b=2d+6b=2d+6 mm for bolt lengths L≤125L≤125 mm, and b=2d+12b=2d+12 mm for L>125L>125 mm. The unthreaded shank diameter equals the nominal thread diameter. Head diameter, head height, square neck length, and square width follow DIN 603 dimensional tables from M5 to M20. Equivalent standards: ISO 8677, BS 4933, NEN 303.

Anti-Rotation Locking
The square neck is designed to seat in a square punched or broached hole. Where a square hole is not practical, the neck may be driven into a round hole with a diameter approximating the square diagonal (about 1.2×d1.2×d). The embedded neck prevents bolt rotation up to the nut’s proof load. In timber connections, the square neck compresses the wood fibres to achieve locking without a pre-formed square hole. The unthreaded shank length should exceed the thickness of the fastened material so that any shear plane intersects the plain shank rather than the threaded section.

Corrosion Protection
Standard finishes include electroplated zinc for indoor and sheltered outdoor use, hot-dip galvanizing for structural and exposed environments, black oxide for appearance and mild protection, and Dacromet for high corrosion resistance and freedom from hydrogen embrittlement in higher-strength classes.

Application Suitability
Used in timber-to-steel, timber-to-timber, and steel-to-steel connections where a smooth round head is required on the finished face and anti-rotation locking is needed on the blind side. Typical applications include wooden structures, fencing, agricultural equipment, machinery guards, and general fabrication. Carbon steel class 8.8 is specified for higher-strength joints; stainless grades are used in food, marine, and architectural applications.