Now to see if I've got one of those taps. Might just use 6mm.
The thread spec isn't that critical, but the diameter is - pick a size that will be a good fit in the holes in the blade disc. Even if you have to enlarge those holes slightly to get a good fit [say 0.5mm clearance on diameter].
Don't want too much slop there, as these bolts take the torsional shock loads when the blades hit something..
