Inch key stock by shaft size: which square or rectangular key a shaft takes, and how deep to cut the keyseat for it.
A key locks a hub — a gear, pulley, sprocket or coupling — to a shaft so the two turn together and the key carries the torque between them. It sits in a keyseat, a rectangular groove cut along the shaft, and in a matching groove (keyway) inside the hub. Key stock is the bar the keys are cut from, sold by its section: square (as wide as it is high) or rectangular. The key size goes by the shaft diameter where the key sits.
| Key width | Shafts over | Through | Square key | Keyseat depth | Rectangular key |
|---|---|---|---|---|---|
| 3/32″ | — | 7/16″ | 3/32″ × 3/32″ | 3/64″ | — |
| 1/8″ | 7/16″ | 9/16″ | 1/8″ × 1/8″ | 1/16″ | — |
| 3/16″ | 9/16″ | 7/8″ | 3/16″ × 3/16″ | 3/32″ | — |
| 1/4″ | 7/8″ | 1-1/4″ | 1/4″ × 1/4″ | 1/8″ | — |
| 5/16″ | 1-1/4″ | 1-3/8″ | 5/16″ × 5/16″ | — | — |
| 3/8″ | 1-3/8″ | 1-3/4″ | 3/8″ × 3/8″ | 3/16″ | — |
| 1/2″ | 1-3/4″ | 2-1/4″ | 1/2″ × 1/2″ | 1/4″ | — |
| 5/8″ | 2-1/4″ | 2-3/4″ | 5/8″ × 5/8″ | 5/16″ | — |
| 3/4″ | 2-3/4″ | 3-1/4″ | 3/4″ × 3/4″ | 3/8″ | — |
| 7/8″ | 3-1/4″ | 3-3/4″ | 7/8″ × 7/8″ | 7/16″ | — |
| 1″ | 3-3/4″ | 4-1/2″ | 1″ × 1″ | 1/2″ | — |
| 1-1/4″ | 4-1/2″ | 5-1/2″ | 1-1/4″ × 1-1/4″ | 5/8″ | — |
| 1-1/2″ | 5-1/2″ | 6-1/2″ | 1-1/2″ × 1-1/2″ | 3/4″ | — |
| 1-3/4″ | 6-1/2″ | 7-1/2″ | — | — | 1-3/4″ × 1-1/2″ |
| 2″ | 7-1/2″ | 9″ | — | — | 2″ × 1-1/2″ |
| 2-1/2″ | 9″ | 11″ | — | — | 2-1/2″ × 1-3/4″ |
| Type | First step | Second step |
|---|---|---|
| Type 1 | 3/16″ × 3/32″ | 1/8″ × 1/16″ |
| Type 1 | 3/8″ × 3/16″ | 5/16″ × 1/8″ |
| Type 1 | 3/8″ × 3/16″ | 5/16″ × 5/32″ |
| Type 1 | 1/2″ × 1/4″ | 7/16″ × 5/32″ |
| Type 1 | 5/8″ × 5/16″ | 3/8″ × 3/16″ |
| Type 1 | 3/4″ × 3/8″ | 1/2″ × 1/4″ |
| Type 1 | 3/4″ × 3/8″ | 5/8″ × 3/16″ |
| Type 1 | 3/4″ × 3/8″ | 5/8″ × 5/16″ |
| Type 1 | 3/4″ × 3/8″ | 11/16″ × 1/4″ |
| Type 1 | 1″ × 1/2″ | 7/8″ × 7/16″ |
| Type 2 | 3/16″ × 3/32″ | 1/4″ × 3/32″ |
| Type 2 | 3/16″ × 3/32″ | 1/4″ × 1/8″ |
| Type 2 | 1/4″ × 1/8″ | 5/16″ × 1/8″ |
| Type 2 | 1/4″ × 1/8″ | 3/8″ × 1/8″ |
| Type 2 | 1/4″ × 1/8″ | 3/8″ × 3/16″ |
| Type 2 | 3/8″ × 3/16″ | 7/16″ × 5/32″ |
| Type 2 | 3/8″ × 3/16″ | 1/2″ × 3/16″ |
| Type 2 | 3/8″ × 3/16″ | 1/2″ × 1/4″ |
| Type 2 | 1/2″ × 1/4″ | 9/16″ × 3/16″ |
| Type 2 | 1/2″ × 1/4″ | 5/8″ × 3/16″ |
| Type 2 | 1/2″ × 1/4″ | 5/8″ × 5/16″ |
| Type 2 | 1/2″ × 1/4″ | 11/16″ × 1/4″ |
| Type 2 | 5/8″ × 5/16″ | 11/16″ × 1/4″ |
| Type 2 | 3/4″ × 3/8″ | 13/16″ × 9/32″ |
| Type 2 | 3/4″ × 3/8″ | 7/8″ × 7/16″ |
| Type 2 | 3/4″ × 3/8″ | 15/16″ × 5/16″ |
| Type 2 | 3/4″ × 3/8″ | 1″ × 1/2″ |
Good to know
Size the key by the shaft. Find the shaft diameter in the two shaft columns; the key width on that row is the standard key for it. On a stepped shaft, go by the diameter where the key sits. A square key sits half in the shaft and half in the hub — the keyseat depth here is the half in the shaft.
Key stock is cut to length and fitted. The sizes here are nominal. Fit tolerances, and how tight the key should be in its keyseat, depend on the stock and the job — use the drawing or the equipment maker’s spec for a critical fit, or give us a call.
Quick answers
- What size key goes on a 1 inch shaft?
- A 1/4″ square key (1/4″ × 1/4″): ASME B17.1 lists it for shafts over 7/8″ through 1-1/4″. The keyseat in the shaft is cut 1/8″ deep.
- What size key stock for a 2 inch shaft?
- 1/2″ square key stock (1/2″ × 1/2″) — for shafts over 1-3/4″ through 2-1/4″, in a keyseat 1/4″ deep in the shaft.
- What shaft size does a 1/4 inch key fit?
- A 1/4″ key is the standard size for shafts over 7/8″ through 1-1/4″.
- How deep is the keyseat for a 3/8 square key?
- 3/16″ in the shaft — half the key’s height, so the other half of the key sits in the hub.
- What is the difference between a key and a keyseat?
- The key is the bar that locks a hub (gear, pulley, sprocket) to a shaft so they turn together. The keyseat is the rectangular groove cut along the shaft, or inside the hub, that the key sits in.