Duravit Starck 3 Water Supply Line Size

[amateurplumb]

Plumber has a 3/8 toilet water supply installed and says he always uses/only carries 3/8 to 7/8 supply lines. My Duravit Starck 3 has a different size on the tank and he says I need to find one that goes from 3/8 to this size.

I attached a photo, but can't find this item from Duravit or the spec for the size. Anyone know what size this should be? Is the right tube one I could find at Home Depot?

Thank you

 

[hj]

The photo tells us NOTHING about the thread size, but so far, I have never seen any other than the standard fill valve thread.