Scope
DIN 931 (the German national standard) was adopted as ISO 4014 with no functional changes — most current drawings reference one or the other interchangeably. The standard covers metric hex head bolts in sizes M1.6 through M64 in product grades A, B, and C. Grade A is tighter tolerance for smaller diameters; Grade B is looser; Grade C is the rough industrial pattern.
The defining feature is partial thread: the bolt has an unthreaded shank between the bearing surface of the head and the start of the threads. This is for shear-loaded joints where the unthreaded shank crosses the shear plane — preventing thread bearing from compromising the joint.
For a fully-threaded metric hex bolt (no shoulder), use DIN 933 / ISO 4017 instead.
How to read the callout
A typical callout looks like:
ISO 4014 - M16 × 80 - 8.8 - HDGThis decodes as:
- ISO 4014 — DIN 931 / ISO 4014 hex head bolt, partial thread
- M16 — 16 mm nominal diameter (coarse pitch implied: M16 × 2.0)
- 80 — 80 mm nominal length
- 8.8 — ISO 898-1 property class (≈ SAE Grade 5)
- HDG — hot-dip galvanized
The thread length (b) is determined from a table keyed off diameter and length — not called out separately. For an M16 × 80 bolt, b = 38 mm; the remaining 42 mm is unthreaded shank.
When to use partial vs full thread
| Joint type | Use |
|---|---|
| Shear-loaded (lateral force across the joint) | DIN 931 (partial thread) — keeps threads out of the shear plane |
| Tension-loaded (joint clamp force only) | Either; DIN 933 (full thread) is often cheaper and stocked deeper |
| Joints where the shank does double duty as a dowel | DIN 931 — the shoulder gives a clean shear surface |
| Long bolts where thread engagement length matters | DIN 933 — full thread maximizes engagement |
Common diameters and lengths stocked
We stock DIN 931 in M6 through M30 in the most common length increments (5 mm steps below M16, 10 mm steps M16–M30). Property class 8.8 is the deepest stock; 10.9 is available in popular sizes; 12.9 is custom on most diameters.
For sizes above M30 (M36, M42, M48, M56, M64), expect a special-order lead time of 2–4 weeks. Property class 10.9 in those sizes is typical.
Related specifications
- ISO 898-1 — Mechanical properties for carbon and alloy steel; pair this with DIN 931 to specify material
- ISO 3506 — Mechanical properties for stainless steel; pair with DIN 931 for stainless bolts
- DIN 933 / ISO 4017 — Fully-threaded metric hex bolt (no shank shoulder)
- DIN 934 / ISO 4032 — Matching metric hex nut