FASTENERS & STANDARDS ·
DIN 931 vs DIN 933: differences, threading and ISO equivalents
DIN 931 refers to partially threaded hexagon head bolts, while DIN 933 refers to fully threaded hexagon head screws. The corresponding international standards are ISO 4014 and ISO 4017. However, the difference is not limited to the thread: when replacing components specified under older DIN standards with their ISO counterparts, the head dimensions must also be checked.
What is the difference between DIN 931 and DIN 933?
| Feature | DIN 931 | DIN 933 |
|---|---|---|
| Thread | Partial: an unthreaded shank section is present | Full: the thread extends close to the head |
| Head | Hexagon | Hexagon |
| Corresponding ISO standard | ISO 4014 | ISO 4017 |
| Selection criterion | Configurations requiring an unthreaded section within the joint | Configurations requiring a longer threaded section |
When should you choose DIN 931 or DIN 933?
DIN 931 is considered when the presence and position of the unthreaded shank are relevant to the joint, for example in relation to the shear planes and the thickness of the assembled components. DIN 933 is considered when the configuration requires a greater threaded length.
Are DIN 931 / ISO 4014 and DIN 933 / ISO 4017 identical?
Not always. DIN and ISO designations are often listed together in catalogues, but certain hexagon head dimensions have changed. One example is dimension s, the width across flats measured between two opposite faces of the head.
DIMENSION s
Dimension s (nominal values in millimetres)
| Diameter | DIN 931 / DIN 933 — s | ISO 4014 / ISO 4017 — s |
|---|---|---|
| M10 | 17 mm | 16 mm |
| M12 | 19 mm | 18 mm |
| M14 | 22 mm | 21 mm |
| M22 | 32 mm | 34 mm |
Practical implication: when a screw must fit into a space-constrained recess, be tightened with specific tools or replace an existing component, checking diameter and length alone is not sufficient: dimension s must also be verified. When moving from DIN to ISO, the hexagon head width across flats decreases for M10, M12 and M14, but increases for M22.
Can a DIN 931 bolt be requested with a special threaded length?
It is possible to request a manufacturing feasibility assessment for hexagon head bolts with a threaded length different from the standard configuration. A clear enquiry should specify the overall length, diameter, thread pitch, actual threaded length, material and mechanical property class.
A special thread configuration must be identified by the agreed dimensions or a technical drawing. It should not automatically be described as identical to the standard version specified by the relevant standard.
Related product pages
DIN 931 and DIN 933 fasteners from Anchor Pro
Anchor Pro manufactures and supplies hexagon head fasteners according to DIN/ISO standards and customer specifications, including requests for special threaded lengths, subject to a feasibility assessment.
Do you need DIN 931, DIN 933 or a special threaded length? Send Anchor Pro the dimensions, material, mechanical property class, quantity and any relevant technical drawing to request a quotation.