Inner dimensions of Waterbox 180.5 flex tubing

[Kato]

I will likely install a Vectra M2 and trying to figure out what the exact dimentions of the hose is. One would think this would be easy to look up, but no luck. Is it 32mm?
I see a 35mm barb fitting for the Vectra M2 what should work then I think.

 

[Kato]

Ah think it’s 28mm