The connecting rod is the connection between the piston and the crankshaft. It joins the piston pin with the crank pin. Small end of the connecting rod is connected to the piston pin and larger end to the crank pin. The function of the connecting rod is to convert linear motion of the piston into rotatory motion of the crankshaft. The connecting rod usually has I-beam cross-section and made of forged steel. Aluminium alloy is also used for connecting rods. They are carefully matched in sets of uniform weight in order to maintain engine balance. The connecting rod carries the power thrust from piston to the crank pin and hence it must be very strong, rigid and also as light as possible.