Thanks Nobby.
M10 that's excellent news! Means I can use exactly the same billet risers I've swapped onto my Jap cruiser as I just love them.
They're made by Aeromach (they supply billet mirrors to WCC and OCC) and are 7" tall, take a 1" bar, and use M10 bolts from underneath.
Yes I know that I'll need longer cables, brake line and wiring...
