DIN 933 dimensions
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.
The DIN number. Superseded by ISO 4017, and still what everyone orders by.
What DIN 933 is
DIN 933 is the fully threaded hex bolt: the thread runs the whole length, right up under the head. It is the bolt most people picture when they say "bolt", and it is the one to use when the joint is clamping through its full depth rather than bearing on a plain shank.
Threaded all the way to the head
The thread on a DIN 933 runs the entire length, right up under the head. That is the whole distinction between this standard and DIN 931, which leaves a plain unthreaded shank under the head, and it decides which one a joint wants.
Full thread is the right choice when the bolt is clamping — pulling two faces together and holding them by friction. Thread engagement is available at any grip length, so one length covers a range of stack-ups, and a DIN 933 bolt that is slightly too long still works because the nut simply runs further down. That flexibility is why a workshop stocks these and reaches for them first.
It is the wrong choice when the joint is loaded across the bolt rather than along it. A thread in shear is being cut at the root, where the section is smallest and the notch is sharpest: an M10 DIN 933 presents roughly 8.5 mm of metal to a shear load — the thread root sits near the diameter the hole was drilled to — where the plain shank of a DIN 931 presents the full 10 mm. That is on the order of 38% more area, in the place where it matters.
DIN 933 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 | 17 mm (ISO 16) | 19.63 mm | 11 mm |
| M12 | 1.75 mm | 19 mm (ISO 18) | 21.94 mm | 13.5 mm |
| M14 | 2 mm | 22 mm (ISO 21) | 25.4 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.
DIN 933 against ISO 4017
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 4017 takes a 16 mm spanner and one made to DIN 933 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 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. Its ISO equivalent is ISO 4017.
Is DIN 933 the same as ISO 4017?
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 DIN 933 take?
17 mm. DIN specifies that size across the flats; the other standard specifies 16 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 DIN 933 still current?
Not formally — DIN 933 has been superseded by ISO 4017. It remains the number everyone uses: catalogues, drawings and purchase orders are still written in DIN numbers, and a supplier asked for DIN 933 will ship a part made to ISO 4017.
Other fastener standards
- ISO 4017 — Hexagon head screws, fully threaded — the ISO standard that replaced DIN 933
- DIN 931 — Hexagon head bolts, partially threaded — a plain shank under the head
- ISO 4014 — Hexagon head bolts, partially threaded — the ISO standard that replaced DIN 931
- 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
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