This is a hose to connect your primary second stage to your first stage. For your personal preference, setup, and dive goal, the hose is available in many different lengths. The shorter lengths can be used, if you are diving with a twin set and use a necklace, and the longer ones provide a bit more slack for single tank diving and ultimately for sidemount and tech diving.
High air flow and a smooth internal bore won't restrict air flow and thus always ensure your ability to breathe easily and smooth. The rubber outer material provides some added weight, so that the hose doesn’t float. It is made to fit most first and second stages on the market.