DIN603 Half Thread Square Neck Carriage Bolts

DIN 603 Half Thread Square Neck Carriage Bolt – Metric Round Head

This metric carriage bolt meets DIN 603 for product grade C, featuring a round mushroom head, a square neck directly under the head, and a partial thread (half thread) configuration. Thread sizes M5 to M20, metric coarse pitch per ISO 261. The square neck embeds into a square or punched hole, providing positive anti-rotation locking during nut tightening from the opposite side. Available in carbon steel (property classes 4.6, 4.8, 8.8, 10.9) and stainless steel (A2-70, A4-80) with finishes including zinc plating, hot-dip galvanizing (HDG), black oxide, or Dacromet.

What are the exact dimensional specifications and thread lengths for DIN 603 half-thread bolts?

Head diameter (dk) ranges from 12.5 mm (M5) to 40.0 mm (M20) ; head height (k) from 3.5 mm (M5) to 11.0 mm (M20) . Square neck length: 5–9 mm depending on diameter, with minimum square width 7.42 mm (M8) . Thread length (b) for half-thread design: for bolt lengths L ≤ 125 mm, b = 2d + 6 mm ; for L > 125 mm, b = 2d + 12 mm . Unthreaded shank diameter equals nominal thread diameter (d) to full ISO tolerance.

What mechanical property values and material grades are required for property class 8.8 and stainless steel versions?

Property class 8.8: minimum tensile strength 800 MPa, yield strength 640 MPa, quenched and tempered from medium-carbon steel (C1038–C1045 or alloyed 10B21). Property class 4.6: tensile 400 MPa, yield 240 MPa from low-carbon steel (C1008–C1022). Stainless A2-70 (304): tensile 700 MPa, proof load 600 MPa; A4-80 (316): tensile 800 MPa, proof load 700 MPa (per ISO 3506-1).

How does the square neck design lock rotation, and what hole geometry is required?

The square neck engages with a square hole (punching or broaching) or a round hole with interference fit of diameter equal to the square’s diagonal (approx. 1.2×d). When inserted, the neck corners embed into the workpiece, preventing bolt rotation at torque values up to the nut’s proof load. For timber, the neck compresses wood fibers to achieve locking without a pre-formed square hole. The unthreaded shank length must exceed the fastened material thickness, ensuring the shear plane (if any) intersects the shank, not the thread.