Btw, thanks for that C clamp trick, that helped out a TON. I built 4 of them. Tacked one underneath to push up, another on top pushing down, pretty much solved my gap issue!
Under the right circumstances a half-C will draw one side up to it's mating surface also.
Those patches on that conical object were placed with half-Cs. It wore rather rapidly since it had a 100mph sand blaster inside it whenever the plant was running. It didn't have to be pretty, just keep the aggregate from escaping.