Diameter of the anti-splash unit on the end of a BlancoOpera6000 tap?

I need to replace the anti-splash unit on the end of a Blanco Opera 6000 tap but I don't know the diameter of it and I'm not in the same house as the tap!

I can't find the tech specs anywhere and I need to place the order so that I have the part ready when I next visit the house. Can anybody help me with a diameter?
Thanks