Stainless steel ball lock carbonation caps with 5/16″ barb. These are intended to convert 1L and 2L bottles to pressurized growlers. Fill up a 1L or 2L PET bottle with your beer. Put one of these on (purge the head space by squeezing if you want to) and then pressurize for transport. You can also use this cap to rapidly carbonate beer. Same process as for transport, just shake it up until it’s carbonated.
Other possible uses… One of these along with some tubing are all you need to convert Mark II Keg and Carboy Washer [Review] to a recirculating draft line cleaning pump for ball lock setups. See: Mark II Keg & Carboy Cleaner… As a Recirculating Draft Line Cleaning Pump! – OR – Build your own line cleaning setup from scratch… Build a Recirculating Draft Line Cleaning Pump