Posted by Martin Cargill on 18/04/2017 08:03:39:
The reason I said blade flange is that some blades use drive pins to stop the blade from tightening and to stop them from spinning off during braking. I see a few of them that have a range of holes to work with different blade pin holes(it's easier to drill a flange than to drill a hole in a blade)
I do understand what your saying and have not ruled out your idea.
The center hole diameter is 11/16 or 17.6mm.