The nuts are 1/4"BSP (British Standard Pipe:-strange old English gas pipe size) with holes and olives to suit 5/16" copper pipe. Also rubber tube with 5/16" bore. Make sure you don't get sold Napoleonic equivalent sizes
Yes we metric boys might spring a leak that wasn't already there when you Brits made the bike in the first place (for 8mm is slightly wider than 5/16")
Hi Mark..If you are planning to have stainless fittings you can buy the correct ones from one of the motorcycle stainless suppliers...Barleycorn Engineering are probably the best on price..or try Lightning Spares. Avoid Phil Pearson (the Goldie specialist) unless you are a wealthy eccentric.
The parts are the same for M20/21/33, B31/33 and Gold Star..Ian