Thus a chain must be "broken" with a chain tool or at a master link (also known as a connecting link) allowing it to be inserted or removed with simple tools for cleaning or replacement.
Thus a chain must be separated, "broken" is a term commonly used, with a chain tool or at a master link. A master link, also known as a connecting link, allows the chain to be inserted or removed with simpler tools, or even no tools, for cleaning or replacement.