Feather key:

• Feather key is a parallel key which is fixed either to the shaft or to the hub (But generally fixed to shaft) and permits relative axial movement between them.
• Feather key permits relative axial movement between shaft and hub as the key is fixed, either in hub or shaft.
• Generally, the feather key is fixed in shaft by screws and a clearance fit is given between key and keyway in hub.

Hence, the correct option is (A).