It's a pig to undo, I can't remember the size offhand. I got it off by holding the hub with a steel pin through one of the holes locked up against the steel housing and smacking the spanner on the nut with a large copper hammer. I'm sure it's a normal thread, mine had been butchered by someone with a chisel previously making it even more fun!Now that we know the idler pullies are left hand metric bolts do you know the size wrench are right or left hand thread for the clutch fan I can not budge it with a adjustable wrench and the clutch spanner
I believe the hub bearing is difficult to source so don't get to brutal!