The Scubapro Superflow 80cm 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. 80CM 0.8m is a longer than normal primary hose for a bit more movement or slack if you run it from a left post on a twin set maybe.