It is the part that connects the piston (to which it is bound by the pin) to the crankshaft and together with the crank of the crankshaft allows the transformation of the rectilinear reciprocating motion of the piston into rotational movement (shaft) . It is one of the most stressed components of the engine. The connecting rods are made of steel, by forging, or spheroidal graphite cast iron (by merger). The two ends of the connecting rod have an eye shape: the one bound to the piston is called “small end”, the one constrained to the crank pin of the crankshaft is called “big end”. The part that connects them is the connecting rod shank. In order to allow the installation of the connecting rod on the shaft, the big end is normally decomposable, provided with rod cap fixed by screws. Usually in the foot end a main bearing is inserted under pressure, on which the piston goes to work. In the head of the piston rod usually two connecting thin conrod bearings are installed.