A shaft is a rotating machine element which is used to transmit power from one place to another. The power is delivered to the shaft by some tangential force and the resultant torque (or twisting moment) setup within the shaft permits the power to be transferred. In order "to transfer the power from one shaft to another", the various members such as pulleys, gears etc. are mounted on it, which cause bending of the shaft.
        Thus, a shaft is used for the transmission of both torque and bending moment.
       They are mainly two type of Shaft:-
● Transmission shaft are used to transmit power between the source and the machine absorbing power. e.g. counter shaft and line shaft.
●Machine shaft is the integral part of machine itself . e.g. crankshaft