ISO 4014 dimensions
Hexagon head bolts, partially threaded — the ISO standard that replaced DIN 931.
The ISO standard. DIN 931 is the DIN number for the same part.
What ISO 4014 is
ISO 4014 covers the same partially threaded hex bolt as DIN 931 and supersedes it. As with the fully threaded pair, the thread is the same and the head is not always.
Why the shank is left plain
A ISO 4014 bolt has a plain, unthreaded shank under the head, and the thread starts partway down. That is the whole distinction between this standard and ISO 4017, which is threaded to the head.
The shank is not a saving of thread-cutting; it is the load-bearing part. Where a joint is loaded across the bolt rather than along it, the shear passes through solid metal instead of through a thread root. An M10 ISO 4014 puts the full 10 mm diameter in the shear plane where a fully threaded bolt puts roughly 8.5 mm — the thread root sits near the diameter the hole was drilled to before tapping. That is on the order of 38% more area, and without the stress raiser that a thread root is.
The shank also locates. A plain cylinder in a reamed hole positions two parts to a fraction of a millimetre; a thread rattling in a clearance hole does not. That is why machine builders specify ISO 4014 for anything that has to go back together in the same place.
The cost is that the grip length matters. The shank has to pass through the joint and the thread has to start beyond it, so a ISO 4014 bolt of the wrong length bottoms the shank against the nut and never clamps — the failure that leaves a joint feeling tight while carrying nothing.
ISO 4014 dimensions, M2 to M24
| Size | Pitch | Across flats | Across corners | Clearance hole |
|---|---|---|---|---|
| M2 | 0.4 mm | 4 mm | 4.62 mm | 2.4 mm |
| M2.5 | 0.45 mm | 5 mm | 5.77 mm | 2.9 mm |
| M3 | 0.5 mm | 5.5 mm | 6.35 mm | 3.4 mm |
| M4 | 0.7 mm | 7 mm | 8.08 mm | 4.5 mm |
| M5 | 0.8 mm | 8 mm | 9.24 mm | 5.5 mm |
| M6 | 1 mm | 10 mm | 11.55 mm | 6.6 mm |
| M8 | 1.25 mm | 13 mm | 15.01 mm | 9 mm |
| M10 | 1.5 mm | 16 mm (DIN 17) | 18.48 mm | 11 mm |
| M12 | 1.75 mm | 18 mm (DIN 19) | 20.78 mm | 13.5 mm |
| M14 | 2 mm | 21 mm (DIN 22) | 24.25 mm | 15.5 mm |
| M16 | 2 mm | 24 mm | 27.71 mm | 17.5 mm |
| M20 | 2.5 mm | 30 mm | 34.64 mm | 22 mm |
| M24 | 3 mm | 36 mm | 41.57 mm | 26 mm |
Across corners is the across-flats divided by cos 30°, which is what a socket has to clear. The standards quote a slightly smaller minimum because the corners may be rounded.
ISO 4014 against DIN 931
The threads are identical and the two are fully interchangeable in the hole. The heads are not identical. At M10, M12, M14 — DIN specifies 17 mm, 19 mm, 22 mm across the flats where ISO specifies 16, 18, 21 mm. Everywhere else in this range the two agree exactly.
That difference is small and extremely annoying. An M10 bolt made to ISO 4014 takes a 16 mm spanner and one made to DIN 931 takes 17 mm. Both are M10, both thread into the same hole, and a socket set built for one will skip a size on the other. It is why metric sets sold today usually carry both 16 and 17.
Frequently asked questions
What is ISO 4014?
Hexagon head bolts, partially threaded — the ISO standard that replaced DIN 931. It is the ISO standard covering the same fastener as DIN 931.
Is ISO 4014 the same as DIN 931?
The threads are the same and the two are interchangeable in the hole, but the heads differ at M10, M12, M14. M10, M12, M14 — DIN specifies 17 mm, 19 mm, 22 mm across the flats where ISO specifies 16, 18, 21 mm. Everywhere else the two agree.
What spanner does an M10 ISO 4014 take?
16 mm. ISO specifies that size across the flats; the other standard specifies 17 mm for the same M10 thread. This is why a socket set that covers 8, 10, 13, 17 and 19 occasionally meets a bolt it cannot grip.
Is ISO 4014 still current?
Yes. ISO 4014 is the current international standard; DIN 931 is the withdrawn German one that preceded it. Suppliers still sell and label parts by the DIN number because that is what customers ask for.
Other fastener standards
- DIN 912 — Hexagon socket head cap screws — the cylindrical head driven by a hex key
- ISO 4762 — Hexagon socket head cap screws — the ISO standard matching DIN 912
- DIN 934 — Hexagon nuts — the plain hex nut
- ISO 4032 — Hexagon regular nuts, style 1 — the ISO standard that replaced DIN 934
- DIN 933 — Hexagon head bolts threaded all the way to the head — DIN’s own title calls these “set screws”, which today reads as a grub screw and is not what this is
Every fastener standard here · Metric thread sizes · Tap drill sizes · Spanner sizes