A chain doesn’t really stretch. Due to poor lubrication, under-sizing or overloading, the pins and bushings actually wear down and become thinner. As they do, the spaces between them increase, making the chain longer and looser.
The offset link is used to lengthen or shorten a length of chain by one pitch. So, it can be used to connect the ends of a new chain that don’t quite reach, or it can be used to take the slack out of an old chain, by replacing one of the original, longer links. Due to its design, the offset link is 35% weaker than the chain itself, so is not recommended for heavy-loaded applications.
Pin diameter and side plate thickness are critical measurements for determining allowable load capabilities.
The correct size of replacement chain to order is determined by three measurements: roller diameter, inside width of roller chain, and the pitch.