Thank you @BrandonM
Sorry - I should have made a better effort to explain my problem.
My homebrew constructions are largely made out of wood, because its practical for me to work.
In order to attach a driven shaft to a wooden component, it is better to have a coupler with more, large, widely spaced fixing points.
In my mind, I know exactly what shaped part I would use
I just don't know what it would be called...