Keyway & parallel key sizes
A 25 mm shaft takes an 8 × 7 mm parallel key, with the keyseat cut 4.0 mm deep into the shaft and 3.3 mm into the hub, per DIN 6885-1 / ISO R773. Enter any shaft diameter and this page returns the standard key cross-section and the two keyseat depths — the lookup you would otherwise do at the machine.
Key width and height step up in bands by shaft diameter, so a nominal shaft size maps to exactly one key. The shaft and hub depths together clear the key height, so the key fits as specified by the standard.
DIN 6885 · shaft >22–30 mm · Normal fit N9/JS9
- Key b × h
- Key width b
- Key height h
- Shaft keyway width
- Shaft keyway width limits
- Hub keyway width
- Hub keyway width limits
- Shaft keyway depth t₁
- Hub keyway depth t₂
- Shaft across the floor d − t₁
- Hub across the keyway d + t₂
- Keyway bottom radius r
- Key chamfer s
How it’s calculated
The row is the one whose shaft range holds the diameter (over its minimum, up to and including its maximum). DIN 6885 writes the first row as over 6 up to 8; a 6 mm shaft takes it, as no smaller row exists. The key is h9 wide and h9 high when square, h11 when rectangular. The fit sets the keyway widths: Free H9 shaft, D10 hub; Normal N9 shaft, JS9 hub; Close P9 both. The depths t₁ and t₂ only go deeper, and drawings dimension them as d − t₁ across the shaft and d + t₂ across the hub.
| Shaft (mm) | Key b × h | Shaft t₁ | Hub t₂ | Standard |
|---|---|---|---|---|
| >12–17 | 5 × 5 | 3 | 2.3 | din_6885 |
| >17–22 | 6 × 6 | 3.5 | 2.8 | din_6885 |
| >22–30 | 8 × 7 | 4 | 3.3 | din_6885 |
| >30–38 | 10 × 8 | 5 | 3.3 | din_6885 |
| >38–44 | 12 × 8 | 5 | 3.3 | din_6885 |
How is keyway size chosen for a shaft?
Parallel-key standards tabulate key width × height against shaft-diameter ranges, not a single diameter — every shaft in a band uses the same key. A 25 mm shaft falls in the >22 to 30 mm band, which calls for an 8 × 7 mm key. The width is machined into the shaft with a keyseat cutter and matched in the hub bore.
Depths are given two ways: the shaft keyseat depth (how deep the slot is cut into the shaft) and the hub keyseat depth. Drawings sometimes dimension the shaft as d − t1 instead of the depth itself; check which convention a print uses before inspecting.