Keyway Size Chart — Inch

What it is

A key locks a hub (pulley, sprocket, gear or coupling) to a shaft so they turn together. The slot in the shaft is the keyseat and the slot in the hub is the keyway. ASME B17.1 sets standard key sizes by shaft diameter. For most inch shafts up to 6-1/2 in, the standard key is square. Rectangular (flat) keys are also listed for thin-wall hubs and larger shafts.

How to use it

1. Measure the shaft diameter with a micrometer.
2. Find the range the diameter falls in. "Over" the lower value, "up to and including" the upper value.
3. Read the square key width and height.
4. Measure the existing key with calipers to confirm. Keystock is sold slightly oversize in some grades so it can be fitted.

Square key chart

Key points

• On a standard square key, about half the key height sits in the shaft and half in the hub. Exact keyseat depths and tolerances are in ASME B17.1.
• Hubs bored by a supplier are usually cut to the standard key for the bore size. Ask for the keyway size if it is not standard.
• Some motor shafts use keys that differ from the table. Check the motor maker's data.
• Key material and fit affect how much torque the joint can carry. That is a design check, not a chart lookup.

Common mistakes

• Choosing a key by the hub keyway alone when the shaft keyseat is worn.
• Grinding down an oversize key unevenly.
• Mixing inch and metric keys. Metric keys (ISO and DIN) follow a different table.

Governing standards: ASME B17.1 (keys and keyseats); ASME B17.2 (Woodruff keys); equipment maker data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.