What are the different types of keys used for shaft-hub connections?

Sunk keys (rectangular, square, and tapered) are most common, fitting into keyways cut in both shaft and hub. Woodruff keys are semi-circular, used for tapered shafts. Saddle keys sit on the shaft without a keyway. Feather keys allow axial sliding while transmitting torque. Splines (internal and external) are used for high torque transmission. Key selection depends on torque magnitude, hub movement requirements, and manufacturing considerations.