The propeller shaft is a steel tube which is used to deliver the transmission output torque (from gearbox) to the differential before it goes to the wheel. It has to cope up with the difference in line and level of the gear box output shaft and differential input shaft.
While transmitting the power, the angle between the axes of the gear box output shaft and the propeller shaft changes continuously. The angle between the propeller shaft axis and the differential input axes also keeps on changes. Hooke’s joint or universal joint are fitted on both ends of the propeller shaft in order to take care of these angle changes.
The effective length of the propeller axis also keeps on changing. To take care of it the propeller shaft has splined ends on which the universal joints are fitted which allows the movement of universal joints along the axis of propeller shaft.
The propeller shaft is designed for high critical speed. The shafts are subject to torsion and shear stress therefore they should be strong enough to bear the stress.