Keyway Dimensions Chart
Parallel key sizes and keyseat depths by shaft diameter: ASME B17.1 square and rectangular keys for inch shafts from 5/16 to 6-1/2 in, and DIN 6885-1 keys for metric shafts from 6 to 110 mm. Jump to inch, depth checks or metric.
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Inch shafts: ASME B17.1 parallel keys
| Shaft dia (in) | Square key W x H | Keyseat depth, shaft and hub | Rectangular key W x H | Keyseat depth, shaft and hub |
|---|---|---|---|---|
| over 5/16 to 7/167.9 to 11.1 mm | 3/32 x 3/322.38 mm | 0.04691.19 mm | Not listed | n/a |
| over 7/16 to 9/1611.1 to 14.3 mm | 1/8 x 1/83.18 mm | 0.06251.59 mm | 1/8 x 3/323.18 x 2.38 mm | 0.04691.19 mm |
| over 9/16 to 7/814.3 to 22.2 mm | 3/16 x 3/164.76 mm | 0.09382.38 mm | 3/16 x 1/84.76 x 3.18 mm | 0.06251.59 mm |
| over 7/8 to 1-1/422.2 to 31.8 mm | 1/4 x 1/46.35 mm | 0.12503.18 mm | 1/4 x 3/166.35 x 4.76 mm | 0.09382.38 mm |
| over 1-1/4 to 1-3/831.8 to 34.9 mm | 5/16 x 5/167.94 mm | 0.15633.97 mm | 5/16 x 1/47.94 x 6.35 mm | 0.12503.18 mm |
| over 1-3/8 to 1-3/434.9 to 44.5 mm | 3/8 x 3/89.53 mm | 0.18754.76 mm | 3/8 x 1/49.53 x 6.35 mm | 0.12503.18 mm |
| over 1-3/4 to 2-1/444.5 to 57.2 mm | 1/2 x 1/212.70 mm | 0.25006.35 mm | 1/2 x 3/812.70 x 9.53 mm | 0.18754.76 mm |
| over 2-1/4 to 2-3/457.2 to 69.9 mm | 5/8 x 5/815.88 mm | 0.31257.94 mm | 5/8 x 7/1615.88 x 11.11 mm | 0.21885.56 mm |
| over 2-3/4 to 3-1/469.9 to 82.6 mm | 3/4 x 3/419.05 mm | 0.37509.53 mm | 3/4 x 1/219.05 x 12.70 mm | 0.25006.35 mm |
| over 3-1/4 to 3-3/482.6 to 95.3 mm | 7/8 x 7/822.23 mm | 0.437511.11 mm | 7/8 x 5/822.23 x 15.88 mm | 0.31257.94 mm |
| over 3-3/4 to 4-1/295.3 to 114.3 mm | 1 x 125.40 mm | 0.500012.70 mm | 1 x 3/425.40 x 19.05 mm | 0.37509.53 mm |
| over 4-1/2 to 5-1/2114.3 to 139.7 mm | 1-1/4 x 1-1/431.75 mm | 0.625015.88 mm | 1-1/4 x 7/831.75 x 22.23 mm | 0.437511.11 mm |
| over 5-1/2 to 6-1/2139.7 to 165.1 mm | 1-1/2 x 1-1/238.10 mm | 0.750019.05 mm | 1-1/2 x 138.10 x 25.40 mm | 0.500012.70 mm |
Ranges are over the first diameter up to and including the second. A parallel key sits half in the shaft and half in the hub, so each keyseat is H/2 deep at its side wall. Published keyseat tables add a small clearance above the key in the hub; check ASME B17.1 for the width and depth tolerances.
Checking depth across the shaft (square keys)
| Shaft dia (in) | Square key | Chordal height Y | Shaft S = D - Y - H/2 | Hub T = D - Y + H/2 |
|---|---|---|---|---|
| 1/2 | 1/8 x 1/8 | 0.00790.20 mm | 0.429610.91 mm | 0.554614.09 mm |
| 3/4 | 3/16 x 3/16 | 0.01190.30 mm | 0.644316.37 mm | 0.831821.13 mm |
| 1 | 1/4 x 1/4 | 0.01590.40 mm | 0.859121.82 mm | 1.109128.17 mm |
| 1-1/4 | 1/4 x 1/4 | 0.01260.32 mm | 1.112428.25 mm | 1.362434.60 mm |
| 1-1/2 | 3/8 x 3/8 | 0.02380.60 mm | 1.288732.73 mm | 1.663742.26 mm |
| 2 | 1/2 x 1/2 | 0.03180.81 mm | 1.718243.64 mm | 2.218256.34 mm |
| 2-1/2 | 5/8 x 5/8 | 0.03971.01 mm | 2.147854.55 mm | 2.772870.43 mm |
| 3 | 3/4 x 3/4 | 0.04761.21 mm | 2.577465.47 mm | 3.327484.52 mm |
S is measured from the keyseat bottom to the far side of the shaft; T from the hub keyseat bottom to the far side of the bore, shown at zero clearance. Y = (D - sqrt(D^2 - W^2)) / 2 is the height of the arc the keyseat removes.
Metric shafts: DIN 6885-1 parallel keys
| Shaft dia (mm) | Key b x h (mm) | Shaft keyseat depth t1 | Hub keyseat depth t2 |
|---|---|---|---|
| over 6 to 80.236 to 0.315 in | 2 x 2 | 1.20.047 in | 1.00.039 in |
| over 8 to 100.315 to 0.394 in | 3 x 3 | 1.80.071 in | 1.40.055 in |
| over 10 to 120.394 to 0.472 in | 4 x 4 | 2.50.098 in | 1.80.071 in |
| over 12 to 170.472 to 0.669 in | 5 x 5 | 3.00.118 in | 2.30.091 in |
| over 17 to 220.669 to 0.866 in | 6 x 6 | 3.50.138 in | 2.80.110 in |
| over 22 to 300.866 to 1.181 in | 8 x 7 | 4.00.157 in | 3.30.130 in |
| over 30 to 381.181 to 1.496 in | 10 x 8 | 5.00.197 in | 3.30.130 in |
| over 38 to 441.496 to 1.732 in | 12 x 8 | 5.00.197 in | 3.30.130 in |
| over 44 to 501.732 to 1.969 in | 14 x 9 | 5.50.217 in | 3.80.150 in |
| over 50 to 581.969 to 2.283 in | 16 x 10 | 6.00.236 in | 4.30.169 in |
| over 58 to 652.283 to 2.559 in | 18 x 11 | 7.00.276 in | 4.40.173 in |
| over 65 to 752.559 to 2.953 in | 20 x 12 | 7.50.295 in | 4.90.193 in |
| over 75 to 852.953 to 3.346 in | 22 x 14 | 9.00.354 in | 5.40.213 in |
| over 85 to 953.346 to 3.740 in | 25 x 14 | 9.00.354 in | 5.40.213 in |
| over 95 to 1103.740 to 4.331 in | 28 x 16 | 10.00.394 in | 6.40.252 in |
DIN 6885-1 sizes. Check the shaft at d - t1 and the hub at d + t2. t1 + t2 runs 0.2 to 0.4 mm more than h, which is the clearance over the top of the key.
Making keyseats
Shaft keyseats are usually milled: an end mill leaves a profile keyseat with round ends, and a side-cutting keyseat cutter leaves a sled-runner keyseat that runs out on a radius and weakens the shaft less at the end. Hub keyways are broached, cut on a slotting or shaping machine, or wire EDM cut when the hub is hardened or the keyway is blind.
Specify the fit, not just the size. The key width tolerance and the keyseat width tolerances together decide whether the key taps in, slides or has to be pressed, and a loose key under reversing load hammers the keyseat walls. Break the edges of the keyseat, and give the key a chamfer so it does not ride on the keyseat fillet.
Frequently asked questions
- What size key for a 1 inch shaft?
- ASME B17.1 puts shafts over 7/8 up to 1-1/4 in on a 1/4 in key: 1/4 x 1/4 square or 1/4 x 3/16 rectangular. The keyseat is 1/8 in deep in the shaft and 1/8 in in the hub for the square key, measured at the side of the keyseat.
- What size key for a 20 mm shaft?
- DIN 6885-1 puts shafts over 17 up to 22 mm on a 6 x 6 key, with a 3.5 mm deep shaft keyseat (t1) and a 2.8 mm deep hub keyseat (t2). Check the shaft at d - t1 = 16.5 mm and the hub at d + t2 = 22.8 mm.
- How do I measure keyseat depth on a round shaft?
- Measure across the shaft from the bottom of the keyseat to the opposite side. For an inch key of width W and height H on a shaft of diameter D, that dimension is S = D - Y - H/2, where the chordal height Y = (D - sqrt(D^2 - W^2)) / 2. For a 1 in shaft with a 1/4 in square key, S = 0.859 in.
- Square or rectangular key?
- Square keys are the default and carry the most torque for a given width. Rectangular keys are lower, so they cut a shallower keyseat, which suits thin-walled hubs and shafts where the keyseat depth would weaken the section. The key width is the same for both at a given shaft size.
- What tolerance goes on keyway width?
- For DIN 6885 keys (width h9), a normal fit uses N9 on the shaft keyseat and JS9 on the hub; a tight fit uses P9 on both; a sliding fit uses H9 on the shaft and D10 on the hub. ASME B17.1 defines class 1 (clearance) and class 2 (closer) fits for inch keys; check the standard for the width limits.
