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Keyway Fit Spec Table
Keyway Fit KS Specifications — 6 sizes
KS B 1311
Fit tolerance table for shaft and hub keyways relative to key width (b). Uses N9/JS9 (transition fit) or H7/h6 (clearance fit) combinations to balance assembly ease and torque transmission.
Practical Notes
- Use P9 (interference) for heavy shock; N9 or Js9 (normal) for frequent disassembly.
- Key-hub keyway uses Js9 (normal) or D10 (loose). Excessive hub keyway clearance causes key rattle and wear.
Selection Guide
Key-shaft keyway: N9 (normal) or P9 (interference). Key-hub keyway: Js9 (normal) or D10 (loose). Use P9 for heavy shock loads; N9/Js9 for frequent assembly/disassembly.
KSKeyway Fit
6 sizes| Key Width | Fit | Fit Type | Shaft Tol | Hub Tol | Clearance |
|---|---|---|---|---|---|
| 2~6 | N9/JS9 | Transition Fit | N9 | JS9 | -0.005~+0.010 |
| 8~12 | N9/JS9 | Transition Fit | N9 | JS9 | -0.010~+0.015 |
| 14~20 | N9/JS9 | Transition Fit | N9 | JS9 | -0.015~+0.020 |
| 2~6 | H7/h6 | Clearance Fit | H7 | h6 | 0.010~0.025 |
| 8~12 | H7/h6 | Clearance Fit | H7 | h6 | 0.015~0.035 |
| 14~20 | H7/h6 | Clearance Fit | H7 | h6 | 0.020~0.045 |
Key Features
- Key-shaft keyway: N9 (normal) / P9 (interference); key-hub keyway: Js9 (normal) / D10 (loose) tolerance system
- Normal type allows easy key insertion/removal; interference type prevents key dislodging under shock loads
- Excessive clearance causes key rattle and fretting; excessive interference concentrates shaft stress
Key Applications
High-speed turbine shafts, impact-load press shafts, reciprocating cranks, large blower shafts, mill drive shafts
FAQ
What happens with a loose keyway fit?
The key rattles in the keyway causing fretting wear (micro-vibration wear). Over time, keyway width increases, requiring replacement.