Because the nitrogen gas in the beer gas mix requires being stored under greater pressure than co2, beer gas requires a high pressure tank and regulator. Normally both the tank and regulator have a bigger diameter regulator connector and match-up connection nozzle than a co2 regulator/tank. Also, the high pressure tanks have a female threaded connection nozzle, rather than the male thread connection nozzle of a co2 tank.
Apologies if I'm using the wrong descriptive terms, but I hope you get the picture.