Keyway Dimension Calculator
Standard parallel key and keyway dimensions for a shaft diameter per DIN 6885-1 — key width and height, shaft and hub keyway depths, and the fit-class tolerances. Metric and imperial.
How it works
A parallel (rectangular) key transmits torque between a shaft and a hub through a
slot — the keyway — cut into both. DIN 6885-1 standardises the key cross-section and
keyway depths by shaft diameter range: pick the range your shaft
falls in and you get the key width b, height h, shaft
keyway depth t₁ and hub keyway depth t₂. The shaft is
machined to a depth-under-keyway of d − t₁, and the hub bore over the
keyway is bore + t₂. Using the standard size keeps stock keys, cutters
and broaches interchangeable.
Worked example
A 40 mm shaft falls in the “over 38 to 44 mm” range, so it takes a
12 × 8 mm key. The shaft keyway depth is t₁ = 5.0 mm
(machine the shaft to 35.0 mm under the keyway) and the hub keyway depth is
t₂ = 3.3 mm (bore plus keyway = 43.3 mm). Cut both with a 12 mm-wide
cutter or broach. The calculator returns this directly.
Reference data
DIN 6885-1 parallel keys by shaft diameter. b = width, h = height, t₁ = shaft keyway depth, t₂ = hub keyway depth.
| Shaft Ø (mm) | Key b × h (mm) | Shaft depth t₁ | Hub depth t₂ |
|---|---|---|---|
| > 6 – 8 | 2 × 2 | 1.2 | 1 |
| > 8 – 10 | 3 × 3 | 1.8 | 1.4 |
| > 10 – 12 | 4 × 4 | 2.5 | 1.8 |
| > 12 – 17 | 5 × 5 | 3 | 2.3 |
| > 17 – 22 | 6 × 6 | 3.5 | 2.8 |
| > 22 – 30 | 8 × 7 | 4 | 3.3 |
| > 30 – 38 | 10 × 8 | 5 | 3.3 |
| > 38 – 44 | 12 × 8 | 5 | 3.3 |
| > 44 – 50 | 14 × 9 | 5.5 | 3.8 |
| > 50 – 58 | 16 × 10 | 6 | 4.3 |
| > 58 – 65 | 18 × 11 | 7 | 4.4 |
| > 65 – 75 | 20 × 12 | 7.5 | 4.9 |
| > 75 – 85 | 22 × 14 | 9 | 5.4 |
| > 85 – 95 | 25 × 14 | 9 | 5.4 |
| > 95 – 110 | 28 × 16 | 10 | 6.4 |
| > 110 – 130 | 32 × 18 | 11 | 7.4 |
Source: DIN 6885-1 parallel-key series. Verify against DIN 6885-1 and the part drawing; the fit/tolerance class is specified separately.
Frequently asked questions
- How do I find the right keyway size for a shaft?
- Enter the shaft diameter. DIN 6885-1 assigns a standard parallel key by diameter range — for example a 40 mm shaft takes a 12 × 8 mm key with a 5.0 mm shaft keyway.
- What are t₁ and t₂?
- t₁ is the keyway depth cut into the shaft (from the shaft surface), and t₂ is the keyway depth in the hub (from the bore). Together they accommodate the key height plus running clearance.
- How deep do I cut the keyway in the shaft?
- Cut to a shaft diameter under the keyway of d − t₁. The calculator shows that "shaft Ø under keyway" value so you can set the cutter depth directly.
- What width cutter or broach do I need?
- The cutter or broach width equals the key width b — 12 mm for the 40 mm shaft example.
- Which fit class should I use?
- Normal (shaft N9 / hub JS9) is the usual choice. Use Free (H9/D10) for guided or sliding keys, and Close (P9/P9) for reversing or shock loads. The fit sets the width tolerance, not the nominal size.
- Is this DIN or ANSI?
- This uses the DIN 6885-1 metric parallel-key series. ANSI inch keys (ASME B17.1) use different sizes; toggle to imperial to read the DIN dimensions in inches.
Method & assumptions
- Parallel (rectangular) keys per DIN 6885-1; Woodruff, tapered and gib-head keys differ.
- The fit class sets width tolerances (free H9/D10, normal N9/JS9, close P9/P9); the nominal key and keyway sizes are the same across fits.
- Torque capacity (shear and bearing on the key) is a separate check — a long enough key for the load.
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