What I thought was to cut the gas pipe off (with German Regulator on) at the bottle end and and slide the pipe over the English Regulator securing with a Jubilee but, the german pipe is to fat to fit over the regulator

My question is I have the 3 taps on mine 2 red 1 yellow the nut on the pipe going to these is 17mm is this a standard size?? has anyone got the same fittings on there bus? It says Truma on them, if so could they check for me if 17mm.
I have a horrible feeling with it being German it may be different so I would be B*****s
I know you can buy propane hoses but 17mm nut adapter to gas taps?????