The pins (#3) are the part of a chain that are most prone to damage. They are actually composed of several pieces, as shown in the diagram below:
Roller chains are the most commonly-used style of chain in production and assembly environments. In the case of roller chains, it refers to deformation of one or more of the several pieces that make up a chain. The phenomenon of chain stretch is more properly referred to as chain elongation, since it is not the case that the chain links themselves are actually getting longer. Although chains are frequently described as having stretched due to wear and use, the term “chain stretch” is slightly misleading.
