I’m using some 7mm braided fuel line for a VW.  It’s really great hose, but it does need a slightly larger clamp given the larger outside diameter of the braided hose.  I use the 7mm because the nipple on my Keihin PWK38 carb is only 6mm.  My raptor-like petcock valve has an 8mm nipple.  So 7mm is a happy in between.  I have a plethora of hose clamps so I just find the best fit.  The small worm gear clamps work good; just don’t over tighten and grind it through the fuel line (another reason I like the braided fuel line - it’s tough and protects the underlying hose).