A hollow saddle key is

A. A taper key which fits half in the key way of hub and half in the key way of shaft

B. A taper key which fits in a key way of the hub and is flat on the shaft

C. A taper key which fits in a key way of the hub and the bottom of the key is shaped to fit the curved surface of the shaft

D. Provided in pairs at right angles and each key is to withstand torsion in one direction only