Some Machining

[Ellis]

I don't really understand. All you'd gain by making the bore of the pulley a hex is moving where you have the setscrews. The Banebots adapter attaches with just setscrews, so, why not attach the pulley in the same way, directly? And, by burying one in the toothed portion of the pulley, as well as its boss, you could have a much sturdier pair of grubs than the BB adapter gives.

Or, probably the best method in terms of balancing work/cost, is a 19mm steel hex piece turned to have a hex portion for the wheel, and a round portion with a large flat onto which you can setscrew the pulley. Much, much easier to machine.