A feather key is generally

Feather key is a special type of key used when one component (like a gear, pulley, or coupling) is required to slide along the shaft while still transmitting torque.

Reason: To allow axial movement, the key is made loose in the shaft so it can slide along with the component, but it is tight in the hub to ensure a firm torque-transmitting connection.

Other options:
- Tight in shaft and loose in hub would prevent sliding, defeating the purpose of a feather key.

- Tight in both shaft and hub would act like a sunk key and not allow axial movement.

- Loose in both shaft and hub would result in no proper torque transmission.

Conclusion: Therefore, a feather key is generally loose in the shaft and tight in the hub.