The 8mm male quick connect to Female DIN Adapter allows you to convert the common 8mm Quick Disconnect Pump or Air Compressor fitting (found on Benjamin/Crosman) into the DIN threads to allow you to use your European gun adapters to fill your CA cylinders.
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.