You know, like the chuck on a metal lathe but smaller. A simple attachment for a cordless drill so that it can hold larger diameter objects like rods for turning.
I will look. Seems like it should be there. In the meantime, I'm making a specific diameter part with a 3D printer.
If you just want a clamp over a rod, weld (or otherwise affix) a shaft to a black-iron pipe cap (or other cup-shaped object) and drill/tap three holes in the cap, at 120 degree separation, so that three bolts can be tightened on a workpiece. Crude, but effective (the shaft fits into your drill's three-jaw chuck, of course).
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