Reference & Charts
Keyway Dimensions
Pick the right key and keyseat for a shaft: the standard ANSI B17.1 square key size for each shaft-diameter range, with the keyseat depth cut into the shaft. From 5/16" up to 4-1/2" shafts, in inches.
11 entries · Last verified: 2026-07-10
A parallel key transmits torque between a shaft and a hub by seating in a slot (keyseat) cut into both. ANSI B17.1 sets the standard square key size for each shaft-diameter range — bigger shafts carry bigger keys. A square key sits half in the shaft and half in the hub, so the keyseat depth cut into the shaft is half the key height (e.g. a 1/4" key needs a 1/8" deep keyseat). Use this table to pick the key, then cut the keyseat to the standard width and depth for your fit.
| Shaft Range | Shaft dia (over–incl.) | Square key (W×H) | Keyseat depth (shaft)(in) |
|---|---|---|---|
| 5/16" – 7/16" | 5/16 to 7/16" | 3/32" sq | 0.047 in |
| 7/16" – 9/16" | 7/16 to 9/16" | 1/8" sq | 0.0625 in |
| 9/16" – 7/8" | 9/16 to 7/8" | 3/16" sq | 0.094 in |
| 7/8" – 1-1/4" | 7/8 to 1-1/4" | 1/4" sq | 0.125 in |
| 1-1/4" – 1-3/8" | 1-1/4 to 1-3/8" | 5/16" sq | 0.156 in |
| 1-3/8" – 1-3/4" | 1-3/8 to 1-3/4" | 3/8" sq | 0.188 in |
| 1-3/4" – 2-1/4" | 1-3/4 to 2-1/4" | 1/2" sq | 0.25 in |
| 2-1/4" – 2-3/4" | 2-1/4 to 2-3/4" | 5/8" sq | 0.313 in |
| 2-3/4" – 3-1/4" | 2-3/4 to 3-1/4" | 3/4" sq | 0.375 in |
| 3-1/4" – 3-3/4" | 3-1/4 to 3-3/4" | 7/8" sq | 0.438 in |
| 3-3/4" – 4-1/2" | 3-3/4 to 4-1/2" | 1" sq | 0.5 in |
Frequently asked
- How deep is the keyseat in the shaft?
- For a square key it's half the key height — the key sits half in the shaft and half in the hub. A 1/4" square key needs a 1/8" deep keyseat in the shaft; a 1/2" key needs 1/4". This chart lists the shaft keyseat depth for each size.
- What key size do I use for a 1-inch shaft?
- A 1" shaft falls in the 7/8"–1-1/4" range, which takes a 1/4" square key with a 1/8" deep keyseat in the shaft. Always select the key from the shaft-diameter range, not the hub.
- Are these square or rectangular keys?
- These are the standard square keys (width = height). ANSI B17.1 also defines rectangular keys (a shorter height) for larger shafts where a full square key would be too deep; the width selection is the same, but the height and keyseat depth differ.
Sources
- ANSI B17.1 — Keys and Keyseats (square parallel key size vs shaft diameter)