DIN 961 Hexagon Head Bolts Fully Threaded with Metric Fine Pitch and Property

DIN 961 Hexagon Head Bolts – Metric Fine Pitch, Fully Threaded, M8 to M24

This product is a metric hexagon head bolt manufactured to DIN 961 (withdrawn, superseded by ISO 8676), featuring a fully threaded shank with metric fine pitch thread. Thread sizes range from M8 to M24 with fine pitches including M8×1, M10×1 or M10×1.25, M12×1.25 or M12×1.5, M14×1.5, M16×1.5, M20×1.5, and M24×2. Manufactured from medium carbon steel, quenched and tempered to property classes 8.8, 10.9, and 12.9 per ISO 898-1, delivering minimum tensile strengths of 800 MPa (8.8) and 1,040 MPa (10.9). Thread tolerance class is 6g per DIN 13 (ISO 965). The fully threaded configuration with fine pitch provides superior vibration resistance, higher stripping strength due to the larger minor diameter, and precise torque control for high-clamping-force applications. Available with zinc plating (clear, blue, yellow), black oxide, hot-dip galvanizing, Dacromet, and Geomet finishes. Widely used in automotive engines, hydraulic systems, high-pressure fluid connections, and precision machinery.

What are the exact dimensional specifications and product grades for DIN 961 M8–M24 fine pitch bolts?

Product grade A applies to threads up to M24 with nominal lengths ≤ 10d or 150 mm (whichever is shorter); grade B applies to lengths exceeding those limits. Key dimensions include: width across flats (s) for M8 = 13.0 mm, M10 = 17.0 mm, M12 = 19.0 mm, M14 = 22.0 mm, M16 = 24.0 mm, M20 = 30.0 mm, M24 = 36.0 mm. Head height (k) ranges from 5.3 mm (M8) to 15.0 mm (M24); for M10, k = 6.4 mm; M12, k = 7.5 mm; M16, k = 10.18 mm. Thread length equals the full bolt length under the head. ISO 8676 supersedes DIN 961 with changed spanner widths for M10, M12, M14, and M22. Critically, M10, M12, and M14 sizes are only available in DIN 961, as ISO 8676 does not cover these diameters with fine pitch.

What are the mechanical property requirements for property classes 8.8, 10.9, and 12.9?

Property class 8.8 bolts are manufactured from medium carbon steel, quenched and tempered per ISO 898-1, with minimum tensile strength of 800 MPa, minimum yield strength of 640 MPa, and hardness range of HRC 22–32. Property class 10.9 bolts are manufactured from alloy steel, quenched and tempered, with minimum tensile strength of 1,040 MPa, minimum yield strength of 940 MPa, and hardness range of HRC 32–39. Property class 12.9 is also available for applications requiring maximum strength. The standard specifies a defined coefficient of friction μ(total) = 0.12–0.18 for elements with nominal tensile strength ≥ 800 MPa. Thread tolerance is 6g for plain finish and 6h for plated finish.

Why is the fine pitch thread specified, and how does the fully threaded design affect performance?

The metric fine pitch thread (pitch values of 1.0–2.0 mm versus coarse pitch of 1.25–3.0 mm) provides three measurable engineering advantages: (1) Higher stripping strength — the larger minor diameter (stress area) of a fine thread increases thread shear area by approximately 8–12% compared to coarse thread of the same nominal diameter; (2) Superior vibration resistance — the shallower helix angle (typically 2–3° versus 3–5° for coarse thread) reduces the tendency for self-loosening under dynamic loading; (3) Precise torque control — the finer thread requires lower tightening torque for the same preload, enabling more accurate torque-tension relationships in critical assemblies. The fully threaded configuration allows load distribution along the entire shank, making it optimal for pre-tapped blind holes and variable grip-length assemblies where maximum thread engagement is required. However, for shear-critical structural joints, a partial-thread variant (DIN 960) is preferred to position the unthreaded shank across shear planes.