Tooling and hardware
Keyway dimensions: key and keyseat sizes by shaft diameter
Inch square and rectangular parallel keys (ASME B17.1), shaft diameters over 5/16 in to 6 1/2 in, and metric DIN 6885-1 keys for shafts over 6 mm to 50 mm. A 1 in shaft takes a 1/4 in square key; cut the keyseat 0.1409 in deep from the top of the shaft.
Technical review pending. Formulas and values are cited. This notice comes down after a machinist review.
| Shaft diameter over (in) | To and including (in) | Square key W x H (in) | Rectangular key W x H (in) |
|---|---|---|---|
| 5/16 | 7/16 | 3/32 x 3/32 | - |
| 7/16 | 9/16 | 1/8 x 1/8 | 1/8 x 3/32 |
| 9/16 | 7/8 | 3/16 x 3/16 | 3/16 x 1/8 |
| 7/8 | 1 1/4 | 1/4 x 1/4 | 1/4 x 3/16 |
| 1 1/4 | 1 3/8 | 5/16 x 5/16 | 5/16 x 1/4 |
| 1 3/8 | 1 3/4 | 3/8 x 3/8 | 3/8 x 1/4 |
| 1 3/4 | 2 1/4 | 1/2 x 1/2 | 1/2 x 3/8 |
| 2 1/4 | 2 3/4 | 5/8 x 5/8 | 5/8 x 7/16 |
| 2 3/4 | 3 1/4 | 3/4 x 3/4 | 3/4 x 1/2 |
| 3 1/4 | 3 3/4 | 7/8 x 7/8 | 7/8 x 5/8 |
| 3 3/4 | 4 1/2 | 1 x 1 | 1 x 3/4 |
| 4 1/2 | 5 1/2 | 1 1/4 x 1 1/4 | 1 1/4 x 7/8 |
| 5 1/2 | 6 1/2 | 1 1/2 x 1 1/2 | 1 1/2 x 1 |
W is the key width, H the key height. A shaft at the upper limit of a range takes that row; a shaft over it takes the next row. A dash means ASME B17.1 lists no rectangular key for that range; use the square key.
Source: ANSI/ASME B17.1 (keys and keyseats), as tabulated in Hoffman, Shop Reference for Students and Apprentices, 2nd ed. (Industrial Press), and the National Machine Tool Co. key size chart; Machinery's Handbook (keyseat depth and chordal height).
| Shaft diameter over (mm) | To and including (mm) | Key b x h (mm) | Shaft keyseat depth t1 (mm) | Hub keyway depth t2 (mm) |
|---|---|---|---|---|
| 6 | 8 | 2 x 2 | 1.2 | 1.0 |
| 8 | 10 | 3 x 3 | 1.8 | 1.4 |
| 10 | 12 | 4 x 4 | 2.5 | 1.8 |
| 12 | 17 | 5 x 5 | 3.0 | 2.3 |
| 17 | 22 | 6 x 6 | 3.5 | 2.8 |
| 22 | 30 | 8 x 7 | 4.0 | 3.3 |
| 30 | 38 | 10 x 8 | 5.0 | 3.3 |
| 38 | 44 | 12 x 8 | 5.0 | 3.3 |
| 44 | 50 | 14 x 9 | 5.5 | 3.8 |
b is the key width, h the key height, d the shaft diameter. t1 is the shaft keyseat depth and t2 the hub keyway depth: the shaft measures d - t1 from the keyseat floor across, and the hub measures d + t2 from the keyway floor across the bore. Depth tolerance: +0.1 mm through 6 x 6 keys, +0.2 mm from 8 x 7 up.
Source: DIN 6885-1 (parallel keys), as published in Elesa+Ganter technical data A16 and the J.W. Winco DIN 6885 keyway table.
How to read the table
Find the range that holds your shaft diameter and read the key size. A 1 in shaft sits in the over 7/8 in to 1 1/4 in row: 1/4 x 1/4 in square or 1/4 x 3/16 in rectangular. The keyseat in the shaft is cut to half the key height at the side wall. A 20 mm shaft sits in the over 17 mm to 22 mm metric row: a 6 x 6 mm key with t1 3.5 mm, so the shaft measures 20 - 3.5 = 16.5 mm over the keyseat. Table sizes are the standard's recommendation; the drawing governs.
Shaft keyseat depth
Depth of cut from the top of the shaft
in
depth = Y + H / 2 = 0.0159 + 0.25 / 2 = 0.1409 in
Touch off on the top of the shaft, then feed down this far. Key from the table: 1/4 x 1/4 in square.
Shaft dimension S, keyseat floor to far side
in
S = D - Y - H / 2 = 1 - 0.0159 - 0.25 / 2 = 0.8591 in
Measure with a micrometer from the keyseat floor across the shaft.
Chordal height Y
in
Y = (D - sqrt(D^2 - W^2)) / 2 = (1 - sqrt(1^2 - 0.25^2)) / 2 = 0.0159 in
How it works
Y = (D - sqrt(D^2 - W^2)) / 2; S = D - Y - H / 2; depth = Y + H / 2
| Symbol | Meaning | Unit |
|---|---|---|
| D | Shaft diameter | in |
| W | Key width | in |
| H | Key height | in |
| Y | Chordal height: shaft surface above the keyseat edge | in |
| S | Dimension over the shaft from the keyseat floor to the far side | in |
| depth | Depth of cut from first touch at the top of the shaft | in |
The keyseat is H / 2 deep at the side wall. Because the shaft is round, the top of the shaft sits Y above that wall, so the cutter feeds Y + H / 2 from first touch.
Worked example: 1.000 in shaft, 1/4 in square key
D = 1.000 in, W = 0.250 in, H = 0.250 in.
- Y = (1.000 - sqrt(1.000 - 0.0625)) / 2 = (1.000 - 0.9682) / 2 = 0.0159 in.
- S = 1.000 - 0.0159 - 0.125 = 0.8591 in.
- Depth from top = 0.0159 + 0.125 = 0.1409 in.
Result: feed 0.1409 in from the top; the shaft measures 0.8591 in over the keyseat.
Worked example: 2.000 in shaft, 1/2 in square key
D = 2.000 in, W = 0.500 in, H = 0.500 in.
- Y = (2.000 - sqrt(4.000 - 0.250)) / 2 = (2.000 - 1.9365) / 2 = 0.0318 in.
- S = 2.000 - 0.031754 - 0.250 = 1.7182 in.
- Depth from top = 0.031754 + 0.250 = 0.2818 in.
Result: feed 0.2818 in from the top; the shaft measures 1.7182 in over the keyseat.
Worked example: 1.000 in shaft, 1/4 x 3/16 in rectangular key
D = 1.000 in, W = 0.250 in, H = 0.1875 in.
- Y = 0.0159 in, the same as the square key (it depends on W only).
- S = 1.000 - 0.015877 - 0.09375 = 0.8904 in.
- Depth from top = 0.015877 + 0.09375 = 0.1096 in.
Result: feed 0.1096 in from the top; the shaft measures 0.8904 in over the keyseat.
Shop notes
- S is the number to check: measure from the keyseat floor across the shaft with a micrometer.
- Table sizes are the standard's recommendation. The drawing governs key size and keyseat depth.
- Inch hub keyseat depth is not calculated on this page. Metric hub depth t2 is in the DIN 6885-1 table.
- The calculator works in inches. For a metric key, read t1 from the DIN table and check the shaft over the keyseat at d - t1.
- Woodruff keys use a separate table; that page is coming.
FAQ
What size key for a 1 in shaft?
A 1/4 in square key (shafts over 7/8 in to 1 1/4 in), or a 1/4 x 3/16 in rectangular key.
How deep is a keyseat for a 1/4 in key on a 1 in shaft?
0.125 in at the side wall; 0.1409 in from the top of the shaft, including the 0.0159 in chordal height.
What should a 1 in shaft measure over the keyseat?
0.8591 in from the keyseat floor to the far side of the shaft, for a 1/4 in square key.
What key for a 20 mm shaft?
A 6 x 6 mm parallel key per DIN 6885-1 (shafts over 17 to 22 mm): shaft keyseat depth t1 3.5 mm, hub depth t2 2.8 mm.
Why is the depth from the top more than half the key?
The shaft curves away from the keyseat edges. The chordal height Y adds to the cut when you touch off on the top of the shaft.
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