The Scubapro Superflow 120cm Hose is a high airflow hose for your regulator with a large, smooth internal bore so it won't restrict air flow. The rubber outer shell both protects the inner hose and adds some weight to the hose so they don't float in the water. 3/8" male thread will fit most regulator 1st stages today (except some Mares and older Apeks that use a 1/2" thread but you can read more about thread sizes here) and the female end is the universal 9/16” that fit all second stages without a swivel or special connection. The female end is fitted with a high torque nut that requires a special tool to tighten properly. 120CM 1.2m is a longer alternate hose to give you and your buddy a bit more space in an out of air situation without too much slack on a traditional setup. Longer hoses like the 1.5m that is prefered for a long hose primary donate setup on a single cylinder but for a single cylinder alternate donate 1.2m is a good long option.