6mm aren’t necessarily 6mm on Amazon. And when they do fit, they’re not ideal. Typically a hazard for snapping off the rod at the base, so it’s used like a key instead of a perma knob. Presently have another one, but it is 7mm.

I think I’m going to mill one out of wood, drill a hole, place tape across part of that hole, and use resin to make the flat half. Which is ridiculous and tiresome.