DIN 940 Double End Studs

DIN 940 double end studs have threads at both ends and a plain shank between them. The metal-end thread length is approximately 2.5d, the longest of the DIN double-end stud series. That length is not arbitrary: it is designed for aluminium and other low-strength light alloys, where the parent material’s shear strength is a fraction of steel’s. In these materials, a standard engagement length can strip the internal thread long before the stud reaches its rated load. The 2.5d metal end spreads the load over a larger shear area, matching the joint’s pull-out resistance to the stud’s own tensile capacity.

This makes DIN 940 the appropriate choice when the tapped component is made of aluminium or another light alloy. By contrast, DIN 938 (1d) suits steel housings, and DIN 939 (1.25d) suits grey cast iron. The 2.5d engagement is long enough that the stud does not bottom out in thin-walled aluminium castings, which is a common failure mode with shorter engagement standards in low-strength materials.

The standard’s scope is narrower than the other DIN studs: it covers M4 to M24 coarse threads and M8×1 to M24×2 fine threads, product grade A. The metal-end thread is produced with a close tolerance fit — either Sk6 or Sn4, depending on whether a plain or fine-pitch thread is specified — to maintain engagement in the softer parent material. Steel versions are available in property classes 5.6, 8.8, and 10.9; stainless versions in A2-70, A4-70, and A4-80. Nominal lengths run up to 200 mm for the larger diameters, with b₂ (nut-end thread) increasing in stages as length grows.

Typical installations include aluminium pump and compressor housings, valve bodies in light-alloy castings, and equipment where a steel stud must be permanently fixed into an aluminium component while the clamped part is removed and refitted repeatedly. In catalogues, these are also listed as double-ended studs, double end stud bolts, or metal-end studs. The selection consideration specific to DIN 940 is whether the tapped hole depth in the light-alloy component is sufficient to accommodate the 2.5d metal end without the stud protruding through the back wall.