DIN 933 vs ISO 4014 vs DIN 931: which hex bolt do you actually need?
"DIN 933 or ISO 4014?" is one of the most common specification questions we are asked — and one of the most common sources of disputes, because the two are frequently treated as interchangeable when they are not.
The short answer
| Standard | Thread | Equivalent | Use when |
|---|---|---|---|
| DIN 933 | Fully threaded to the head | ISO 4017 | The load is carried by the thread, or the joint thickness is variable |
| ISO 4014 | Partially threaded | DIN 931 | The shank must carry shear, or a defined unthreaded length is required |
| DIN 931 | Partially threaded | ISO 4014 | As above, for specifications written to DIN |
Why the distinction actually matters
A partially threaded bolt has an unthreaded shank of approximately the nominal diameter, whereas a fully threaded bolt has a reduced thread core diameter along its whole length. Two consequences follow:
- Shear capacity. Where a joint is loaded in shear, the unthreaded shank of a partially threaded bolt sits in the shear plane and carries considerably more load than the threaded core of an equivalent fully threaded bolt. Substituting DIN 933 for ISO 4014 in a shear-critical connection reduces capacity without changing appearance.
- Bearing area and hole fit. The full-diameter shank also gives a tighter fit in the hole, which matters where the joint relies on bearing rather than friction.
How to decide in practice
- Read what the drawing specifies. If it says ISO 4014, do not accept an ISO 4017 substitute without an engineering sign-off — and if it says "hex bolt M12 × 60", ask which.
- Check the joint thickness range. Fully threaded bolts tolerate a wider range of clamped thicknesses because there is always thread where the nut lands. Partially threaded bolts need the unthreaded shank to sit inside the joint, so the clamped thickness must fall within a defined band.
- Identify the design load case. Tension through the thread favours neither. Shear through the shank favours the partially threaded form.
- Check the standard chain. If the specification is written to DIN 931/933, quoting ISO 4014/4017 requires a cross-reference note on the certificate, even where the dimensions agree.
Head dimensions and the third variable
DIN and ISO differ subtly in head dimensions and in the width across corners, and ASME B18.2.1 is a different family again. For most applications the difference is irrelevant. Where socket access is tight, where a specific washer diameter is used, or where an automated feeder is set up around one head geometry, it is not. This is one of the reasons we ask for a drawing rather than a description.
What we recommend
- Structural steelwork: check the connection design. Most modern European design is written to EN 15048 or EN 14399, which reference ISO threads rather than DIN.
- Machinery and general assembly: fully threaded hex bolts are easier to stock because they suit a wider range of joint thicknesses.
- Shear-critical joints: partially threaded, with the unthreaded shank verified in the shear plane.
- When in doubt: send the drawing. We will tell you which standard it calls for, produce to it, and state the standard on the inspection report.