CEJN Fittings CEJN fittings are common on many rebreather systems. CEJN is the same as the Apeks inflators. The reason CEJN is used on the systems instead of a standard BC fitting is flow rates. A standard BC nipple will not allow enough flow through for use with bail out valves. For safety most rebreather divers convert all their fittings over to the same thread so in an emergency they can plug their off-board gas into anywhere they need it.