Keyway & Key Size Chart
Square key, rectangular key, and Woodruff key dimensions by shaft diameter. Covers ANSI B17.1 (inch), DIN 6885 / ISO 2491 (metric), and Woodruff standard sizes with keyway depth for shaft and hub.
Reference
Keys transmit torque between a shaft and a hub (gear, pulley, sprocket). Square and rectangular parallel keys sit in matching keyways on the shaft OD and hub ID. Woodruff keys are half-moon — the keyway is milled with a circular cutter and the key self-locates, ideal for tapered shafts. This chart gives the standard key cross-sections, the keyway width, and the depths cut into shaft and hub for class-II (free) fit. For interference fits, reduce keyway depth by 0.002" / 0.05 mm.
ANSI B17.1 — square & rectangular parallel keys (inch)
| Shaft Ø (in) | Key W × H | Keyway W | Shaft depth (T) | Hub depth (T₁) | Type |
|---|---|---|---|---|---|
| 5/16 - 7/16 | 3/32 × 3/32 | 3/32 | 3/64 | 3/64 | Square |
| 7/16 - 9/16 | 1/8 × 3/32 | 1/8 | 3/64 | 1/32 | Rectangular |
| 7/16 - 9/16 | 1/8 × 1/8 | 1/8 | 1/16 | 1/16 | Square |
| 9/16 - 7/8 | 3/16 × 1/8 | 3/16 | 1/16 | 3/64 | Rectangular |
| 9/16 - 7/8 | 3/16 × 3/16 | 3/16 | 3/32 | 3/32 | Square |
| 7/8 - 1-1/4 | 1/4 × 3/16 | 1/4 | 3/32 | 3/32 | Rectangular |
| 7/8 - 1-1/4 | 1/4 × 1/4 | 1/4 | 1/8 | 1/8 | Square |
| 1-1/4 - 1-3/8 | 5/16 × 1/4 | 5/16 | 1/8 | 1/8 | Rectangular |
| 1-1/4 - 1-3/8 | 5/16 × 5/16 | 5/16 | 5/32 | 5/32 | Square |
| 1-3/8 - 1-3/4 | 3/8 × 1/4 | 3/8 | 1/8 | 1/8 | Rectangular |
| 1-3/8 - 1-3/4 | 3/8 × 3/8 | 3/8 | 3/16 | 3/16 | Square |
| 1-3/4 - 2-1/4 | 1/2 × 3/8 | 1/2 | 3/16 | 3/16 | Rectangular |
| 1-3/4 - 2-1/4 | 1/2 × 1/2 | 1/2 | 1/4 | 1/4 | Square |
| 2-1/4 - 2-3/4 | 5/8 × 7/16 | 5/8 | 7/32 | 7/32 | Rectangular |
| 2-1/4 - 2-3/4 | 5/8 × 5/8 | 5/8 | 5/16 | 5/16 | Square |
| 2-3/4 - 3-1/4 | 3/4 × 1/2 | 3/4 | 1/4 | 1/4 | Rectangular |
| 2-3/4 - 3-1/4 | 3/4 × 3/4 | 3/4 | 3/8 | 3/8 | Square |
| 3-1/4 - 3-3/4 | 7/8 × 5/8 | 7/8 | 5/16 | 5/16 | Rectangular |
| 3-1/4 - 3-3/4 | 7/8 × 7/8 | 7/8 | 7/16 | 7/16 | Square |
| 3-3/4 - 4-1/2 | 1 × 3/4 | 1 | 3/8 | 3/8 | Rectangular |
| 3-3/4 - 4-1/2 | 1 × 1 | 1 | 1/2 | 1/2 | Square |
| 4-1/2 - 5-1/2 | 1-1/4 × 7/8 | 1-1/4 | 7/16 | 7/16 | Rectangular |
| 4-1/2 - 5-1/2 | 1-1/4 × 1-1/4 | 1-1/4 | 5/8 | 5/8 | Square |
| 5-1/2 - 6-1/2 | 1-1/2 × 1 | 1-1/2 | 1/2 | 1/2 | Rectangular |
| 5-1/2 - 6-1/2 | 1-1/2 × 1-1/2 | 1-1/2 | 3/4 | 3/4 | Square |
DIN 6885 / ISO 2491 — metric parallel keys
| Shaft Ø (mm) | Key W × H (mm) | Shaft depth t₁ | Hub depth t₂ | Keyway length |
|---|---|---|---|---|
| 6 - 8 | 2 × 2 | 1.2 | 1.0 | 6 - 20 mm |
| 8 - 10 | 3 × 3 | 1.8 | 1.4 | 6 - 36 mm |
| 10 - 12 | 4 × 4 | 2.5 | 1.8 | 8 - 45 mm |
| 12 - 17 | 5 × 5 | 3.0 | 2.3 | 10 - 56 mm |
| 17 - 22 | 6 × 6 | 3.5 | 2.8 | 14 - 70 mm |
| 22 - 30 | 8 × 7 | 4.0 | 3.3 | 18 - 90 mm |
| 30 - 38 | 10 × 8 | 5.0 | 3.3 | 22 - 110 mm |
| 38 - 44 | 12 × 8 | 5.0 | 3.3 | 28 - 140 mm |
| 44 - 50 | 14 × 9 | 5.5 | 3.8 | 36 - 160 mm |
| 50 - 58 | 16 × 10 | 6.0 | 4.3 | 45 - 180 mm |
| 58 - 65 | 18 × 11 | 7.0 | 4.4 | 50 - 200 mm |
| 65 - 75 | 20 × 12 | 7.5 | 4.9 | 56 - 220 mm |
| 75 - 85 | 22 × 14 | 9.0 | 5.4 | 63 - 250 mm |
| 85 - 95 | 25 × 14 | 9.0 | 5.4 | 70 - 280 mm |
| 95 - 110 | 28 × 16 | 10.0 | 6.4 | 80 - 320 mm |
| 110 - 130 | 32 × 18 | 11.0 | 7.4 | 90 - 360 mm |
Woodruff keys — ANSI B17.2 (inch)
| Key # | Nominal W × B (in) | Full Ø | Shaft depth | Hub depth |
|---|---|---|---|---|
| 204 | 1/16 × 1/2 | 1/2 | 0.0728 | 0.0313 |
| 304 | 3/32 × 1/2 | 1/2 | 0.0638 | 0.0469 |
| 305 | 3/32 × 5/8 | 5/8 | 0.0876 | 0.0469 |
| 404 | 1/8 × 1/2 | 1/2 | 0.0545 | 0.0625 |
| 405 | 1/8 × 5/8 | 5/8 | 0.0788 | 0.0625 |
| 406 | 1/8 × 3/4 | 3/4 | 0.1038 | 0.0625 |
| 505 | 5/32 × 5/8 | 5/8 | 0.0698 | 0.0781 |
| 506 | 5/32 × 3/4 | 3/4 | 0.0948 | 0.0781 |
| 507 | 5/32 × 7/8 | 7/8 | 0.1198 | 0.0781 |
| 606 | 3/16 × 3/4 | 3/4 | 0.0858 | 0.0938 |
| 607 | 3/16 × 7/8 | 7/8 | 0.1108 | 0.0938 |
| 608 | 3/16 × 1 | 1 | 0.1358 | 0.0938 |
| 807 | 1/4 × 7/8 | 7/8 | 0.0928 | 0.1250 |
| 808 | 1/4 × 1 | 1 | 0.1178 | 0.1250 |
| 809 | 1/4 × 1-1/8 | 1-1/8 | 0.1428 | 0.1250 |
| 810 | 1/4 × 1-1/4 | 1-1/4 | 0.1678 | 0.1250 |
| 811 | 1/4 × 1-3/8 | 1-3/8 | 0.1928 | 0.1250 |
| 812 | 1/4 × 1-1/2 | 1-1/2 | 0.2178 | 0.1250 |
| 1210 | 3/8 × 1-1/4 | 1-1/4 | 0.1548 | 0.1875 |
| 1211 | 3/8 × 1-3/8 | 1-3/8 | 0.1798 | 0.1875 |
| 1212 | 3/8 × 1-1/2 | 1-1/2 | 0.2048 | 0.1875 |
Key-number decoding (Woodruff)
- Woodruff key numbers are a compact sizing code: the last two digits × 1/8 = cutter diameter in inches; the preceding digits × 1/32 = nominal key width.
- Example: #808 = 08 × 1/32 = 1/4" wide, 08 × 1/8 = 1" diameter.
- #1210 = 12 × 1/32 = 3/8" wide, 10 × 1/8 = 1-1/4" diameter.
- Metric Woodruff keys use DIN 6888 — sizes given as W × D (mm), e.g. 6 × 22 means 6 mm wide × 22 mm diameter.
Design notes
- Key length: rule of thumb is 1.5 × shaft diameter for full torque transmission. Less = shear / bearing failure; more = rarely a problem.
- For high-speed reversing loads, use two keys 180° apart to balance the shaft.
- Keyway cutting: use a slotting or broaching operation on the hub. For short runs, an end mill in a CNC or slotter is fine.
- Keyway stress-concentration: sharp corners at the keyway ends are a fatigue initiation point. Fillet the ends with a radius ≥ 0.010" (0.25 mm) or cut a sled-runner keyway with lead-in / lead-out.
- Taper keys (gib-head) wedge axially into a tapered keyway; used on older machinery. Forbidden on high-speed rotating equipment because of imbalance.
- Set-screw alternative: for loads below ~20% of key-specified torque, a pair of cup-point set screws at 90° (or one over the keyway + one 90° off) can replace a key on cheap adapters — not for safety-critical drives.
Torque capacity (approximate)
- Shear capacity (steel key)
- T = (W × L × D × Ss) / 2 · Ss = 80 MPa (11.6 ksi) for soft key steel
- Bearing capacity (key sides)
- T = (H × L × D × Sc) / 4 · Sc = 140 MPa (20 ksi) for mild steel
- Typical margin
- Design to 2× max operating torque; use the smaller of shear or bearing calc
- #1 common failure
- Key rolling in keyway from insufficient key length; shaft key ejects axially
- #2 common failure
- Fatigue crack at keyway corner from sharp entry; fillet required
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