Overflow pipe? What's that for. The carb overflow? What is it 10mm? Don't believe it's a specific size. Just measure the outer diameter of the carb. Rubber stretches anyway. Personally I like it a little tight that loose.
I linked you to a ebay page with lots of various sizes on fleabay.
To tell you the truth I never measured it. Just used cable ties and jubilee clips.
As said better to go a little tight than the other way. Just cause the rubber/silicon will stretch a little. but too tight just means it'll come off under preasure.
Found out the stock size for the carb breather pipes are 4mm internal and 2mm wall thickness so anyone wanting coloured pipes to match there bike or coolant pipes that's what you need
