We recently changed the details of our MOT coils (OK, we had to. We messed around and there were … consequences. There was a shotgun involved, as it were) The old MOT coils were wound on a form, which held the wires in place. The new geometry is tighter and required something smaller, so we decided to go with no holder — the wires would be free-standing, but since they had adhesive on them, they would stick together. And we could coat them with epoxy, just to make sure.

But this still required something on which to wind the coils, and in machining terminology, such a device is called a mandrel. Which I immediately named “Barbara.”