In the technical documentation of fasteners, markings often appear DIN 931 and ISO 4014. Both standards describe hexagonal screws with partial thread, therefore in practice they are very often treated as equivalents.
This doesn't mean, however, that they are completely identical. The ISO standard introduced several changes that are worth knowing, especially when designing structures or ordering fasteners.
DIN 931 vs. ISO 4014
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Both standards describe hexagonal screws with partial thread.
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DIN 931 this is the German standard.
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ISO 4014 is the international equivalent.
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In most applications they are interchangeable.
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In some diameters the head size (key size) varies.
The most important difference: head size (turnkey size)
The most important difference between DIN 931 and ISO 4014 concerns screw head size – i.e. key size (s).
In selected diameters the values may differ by approximately 1 mm.
Examples of differences
Diameter DIN 931 ISO 4014 Difference M10 17 mm 16–17 mm approx. 1 mm M12 19 mm 18–19 mm approx. 1 mm M14 22 mm 21–22 mm approx. 1 mm M22 34 mm 32–34 mm approx. 1–2 mm In practice this means that the same screw may require different key size, depending on the standard or manufacturer.
Why do differences matter?
In most standard connections, these differences do not affect the performance of the screw.
However, they may be important in situations such as:
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serial assembly,
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limited turnkey space,
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use of specific attachments or assembly machines.
Therefore, when designing a structure, it is always worth checking the standard of the element used.
Where are DIN 931 / ISO 4014 screws used?
Partially threaded screws are used where the connection must withstand heavy loads.
Most common uses:
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steel structures
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industrial machines
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industrial installations
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energy infrastructure
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supporting structures.
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FAQ – Frequently Asked Questions
Are DIN 931 and ISO 4014 the same screw?
Not quite. The standards describe very similar screws, but they may differ in head dimensions for selected diameters.
Can DIN 931 be replaced by ISO 4014?
In most applications, yes. However, it's worth checking the wrench size in the technical documentation.
Why might the key size be different?
ISO has introduced minor dimensional changes to unify standards and optimize screw design.
When does difference matter?
For serial assembly, in tight assembly spaces or when specific tools are used.
Check out Eurobolt's offer
Are you looking for screws that meet standards? DIN 931 or ISO 4014 for steel structures, machinery, or industrial installations? Eurobolt offers a wide selection of fasteners in various strength classes, materials, and anti-corrosion coatings.
Check out the available products in our offer or contact us if you need help choosing the right solution for your project.
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