The links determine the tensile strength of the chain and engage the sprocket teeth with a sliding motion. The link apertures act as short bearings for the pins to rotate in. To achieve high strength and wear resistance, the links are made of special steel that is heat treated and surface finished.
Guide links appear on both sides of the chain and serve three purposes.
They hold the chain lacing together, prevent it from sliding off the sprocket,
and contribute to the tensile strength.
The pins connect the interleaved rows of links and are press-fitted into the guide links and then riveted. Because the pins rub against the link apertures, they are made of a special steel and heat treated to obtain a high surface hardness. Exceptional surface finish also contributes to the wear resistance of the chain.