Fuel pipe size?

[SeriesLandy]

I'm about to run my fuel lines and just wondering what size I should use.

I've got some 10mm copper pipe that I had in the garage is it ok to use that and change the 8mm barb on the carb to a 10mm one or do I need to run 8mm copper pipe? Does anyone know the thread?

Also do I need to run a return or can I do it later if needs be. Currently running a pinto on standard carb.