Proper Calor regulator nut size?

Just a real quick one, i hope someone can answer before i go away, we're running flo-gas atm, but im gonna start using Calor this weekend.

I have the regulator, and a new bottle, but i've now left the regulator in the 'van in storage, Does anyone know off the top of their head what size the nut is so i can take the correct spanner to fit on site

Many thanks.