# Inch square and rectangular keys to 1-1/2 in (ANSI B17.1): 3/4, 7/8, 1, 1-1/4, 1-1/2 in square, 1/2 x 3/8, 1 x 3/4 in rectangular keys, shaft range and keyseat depth

> What key size goes with a 2 in, 3 in or 4 in shaft (ANSI B17.1): square key width, rectangular key height and keyseat depth?

- Category: Hardware › Gears, cranks & flywheels
- Kind: Standard part
- Basis: ANSI B17.1 shaft-to-key table (Engineers Edge and GlobalSpec agree) with Engineers Edge keyseat S / T depths cross-checked by T - S = H + 0.005; numbers only
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**Exact dimensions.** True size, with no tolerance added.

## Notes

- Keyseat depths in inches from Engineers Edge (nominal shaft: key square / rectangular; S shaft keyseat square and rectangular; T hub keyseat, parallel, square and rectangular): 1-3/4: 3/8 sq / 3/8 x 1/4, S 1.542 / 1.605, T 1.922 / 1.860; 2: 1/2 sq / 1/2 x 3/8, S 1.718 / 1.781, T 2.223 / 2.161; 2-1/4: 1/2 sq / 1/2 x 3/8, S 1.972 / 2.034, T 2.477 / 2.414; 2-1/2: 5/8 sq / 5/8 x 7/16, S 2.148 / 2.242, T 2.778 / 2.684; 3: 3/4 sq / 3/4 x 1/2, S 2.577 / 2.702, T 3.332 / 3.207; 3-1/2: 7/8 sq / 7/8 x 5/8, S 3.007 / 3.132, T 3.887 / 3.762; 4: 1 sq / 1 x 3/4, S 3.436 / 3.561, T 4.441 / 4.316; 5: 1-1/4 sq / 1-1/4 x 7/8, S 4.296 / 4.483, T 5.551 / 5.363; 6: 1-1/2 sq / 1-1/2 x 1, S 5.155 / 5.405, T 6.660 / 6.410.
- An inch parallel key sits half in the shaft keyseat and half in the hub keyseat. ANSI B17.1 gives, for a shaft-diameter range, one key width W, a square height H = W, and a lower rectangular key (height H) that is used on bigger shafts: square keys are preferred up to a 6-1/2 in shaft and rectangular keys for larger ones. The keyseat depth in the shaft (nominal) is H/2. The shaft ranges are 'over x to and including y'; the standard says they identify key sizes and are not meant to set shaft sizes.
- Numbers: the ANSI B17.1 shaft-to-key table as reproduced by Engineers Edge and by GlobalSpec (they agree on every row shown), and Engineers Edge's keyseat-depth table (S = shaft depth measured from the opposite side, T = hub depth) for nominal shafts 1-3/4 to 6 in. The generator checks H = W and keyseat depth = H/2 on the key table and, for every S / T row, T - S = key height + 0.005 in for both the square and the rectangular key, which also confirms which key belongs to which shaft range. The footnote that marks the 1-1/2 x 1-1/2 rectangular key on the 6-1/2 to 7-1/2 shaft is not shown (that size is above this page).
- Numbers only, no files: a key is a plain bar (a box with no published chamfers), and the length is chosen by the user. Square keys up to 1/2 in wide are on the 'Square keys, inch' page with files; this page adds the larger square keys and all the rectangular ones.
- Left out: keys wider than 1-1/2 in, tapered (gib-head) keys, the tolerances on W and H, the S / T values for 1/2 to 1-1/2 in shafts and 7 in and larger (the Engineers Edge table read here starts at 1-3/4), Woodruff keys (their own pages).

## Sizes

| shaft Ø over to (incl.), in | key width W, in (mm) | square key W x H, in (mm) | rectangular key W x H, in (mm) | keyseat depth H/2, square key, in (mm) | keyseat depth H/2, rectangular key, in (mm) |
|---|---|---|---|---|---|
| 5/16 to 7/16 | 3/32 (2.381) | 3/32 x 3/32 (2.381 x 2.381) | none listed | 3/64 (1.191) | — |
| 7/16 to 9/16 | 1/8 (3.175) | 1/8 x 1/8 (3.175 x 3.175) | 1/8 x 3/32 (3.175 x 2.381) | 1/16 (1.588) | 3/64 (1.191) |
| 9/16 to 7/8 | 3/16 (4.763) | 3/16 x 3/16 (4.763 x 4.763) | 3/16 x 1/8 (4.763 x 3.175) | 3/32 (2.381) | 1/16 (1.588) |
| 7/8 to 1-1/4 | 1/4 (6.35) | 1/4 x 1/4 (6.35 x 6.35) | 1/4 x 3/16 (6.35 x 4.763) | 1/8 (3.175) | 3/32 (2.381) |
| 1-1/4 to 1-3/8 | 5/16 (7.938) | 5/16 x 5/16 (7.938 x 7.938) | 5/16 x 1/4 (7.938 x 6.35) | 5/32 (3.969) | 1/8 (3.175) |
| 1-3/8 to 1-3/4 | 3/8 (9.525) | 3/8 x 3/8 (9.525 x 9.525) | 3/8 x 1/4 (9.525 x 6.35) | 3/16 (4.763) | 1/8 (3.175) |
| 1-3/4 to 2-1/4 | 1/2 (12.7) | 1/2 x 1/2 (12.7 x 12.7) | 1/2 x 3/8 (12.7 x 9.525) | 1/4 (6.35) | 3/16 (4.763) |
| 2-1/4 to 2-3/4 | 5/8 (15.875) | 5/8 x 5/8 (15.875 x 15.875) | 5/8 x 7/16 (15.875 x 11.113) | 5/16 (7.938) | 7/32 (5.556) |
| 2-3/4 to 3-1/4 | 3/4 (19.05) | 3/4 x 3/4 (19.05 x 19.05) | 3/4 x 1/2 (19.05 x 12.7) | 3/8 (9.525) | 1/4 (6.35) |
| 3-1/4 to 3-3/4 | 7/8 (22.225) | 7/8 x 7/8 (22.225 x 22.225) | 7/8 x 5/8 (22.225 x 15.875) | 7/16 (11.113) | 5/16 (7.938) |
| 3-3/4 to 4-1/2 | 1 (25.4) | 1 x 1 (25.4 x 25.4) | 1 x 3/4 (25.4 x 19.05) | 1/2 (12.7) | 3/8 (9.525) |
| 4-1/2 to 5-1/2 | 1-1/4 (31.75) | 1-1/4 x 1-1/4 (31.75 x 31.75) | 1-1/4 x 7/8 (31.75 x 22.225) | 5/8 (15.875) | 7/16 (11.113) |
| 5-1/2 to 6-1/2 | 1-1/2 (38.1) | 1-1/2 x 1-1/2 (38.1 x 38.1) | 1-1/2 x 1 (38.1 x 25.4) | 3/4 (19.05) | 1/2 (12.7) |

## Where the files are

- Engineers Edge: [Shaft diameter vs key sizes (ANSI B17.1): W, square H, rectangular H, keyseat depth H/2](https://engineersedge.com/gears/shaft_diameter_vs_key_sizes_14411.htm) — web — Publisher's page; dimensions are facts
- GlobalSpec (ANSI B17.1-1967 R1998 excerpt): [Keys and keyseats: shaft diameter, key width W, height H square and rectangular, keyseat depth H/2](https://www.globalspec.com/reference/77011/203279/keys-and-keyseats) — web — Publisher's page; dimensions are facts
- Engineers Edge: [Shaft and hub keyseat depth S and T for square and rectangular keys (ANSI B17.1), 1-3/4 to 7 in shafts](https://engineersedge.com/gears/shaft_key_seat_depth_14412.htm) — web — Publisher's page; dimensions are facts

## Questions

**What key goes on a 2 in shaft?**

A 1/2 in square key (the 1-3/4 to 2-1/4 in shaft range); the rectangular key is 1/2 wide by 3/8 high. Shaft keyseat depth about H/2 = 1/4 in.

**What key goes on a 3 in shaft?**

A 3/4 in square key (shaft range 2-3/4 to 3-1/4); the rectangular key is 3/4 x 1/2.

**What key goes on a 4 in shaft?**

A 1 in square key (3-3/4 to 4-1/2 range); rectangular 1 x 3/4.

**What is the keyseat depth for a square key?**

H/2, i.e. half the key height: 1/4 in for a 1/2 in square key, 1/2 in for a 1 in square key.

**When are rectangular keys used?**

ANSI B17.1 prefers square keys up to a 6-1/2 in shaft and rectangular keys above that; the rectangular keys are also listed for smaller shafts, with a lower height, where the shaft cannot take the deeper keyseat.

## Fits with

- [Square keys, inch (ANSI B17.1): 3/32 to 1/2 in](https://xemstudio.com/objects/square-keys-inch/)
- [Parallel keys DIN 6885 form A: 2 × 2 to 18 × 11, with keyway depths](https://xemstudio.com/objects/parallel-keys-din-6885/)
- [Woodruff keys, inch (ANSI B17.2): key numbers #202 to #1212, key sizes and keyseat depths](https://xemstudio.com/objects/woodruff-keys-inch-ansi-b17-2/)
- [Woodruff keys, metric (DIN 6888 / ISO 3912): b × h × d2, keyseat depths t1 and t2, shaft ranges](https://xemstudio.com/objects/woodruff-keys-din-6888/)
- [Hex keys (Allen keys): ISO 2936 metric 0.7–36 mm and ASME B18.3 inch .050–7/8 in: across flats, across corners, long and short arm + 31 key models](https://xemstudio.com/objects/hex-keys-iso-2936-asme-b18-3/)