The 8mm Quick-Disconnect Double Male Coupling has the 8mm male stud on both ends allows you to convert the common 8mm female Quick Disconnect Pump or Air Compressor fitting (found on Benjamin/Crosman) to male.
Many Air/Water Filters also use 8mm quick disconnects. This adapter also allows you to utilize various filters in between the pump/compressor and your cylinder to ensure that your cylinders only get pure air.