Bobbin Part Chuck Adapters
You can use these to connect the 2 bobbin parts (A&B) to a drill press chuck to true up the roundness after printing or to enlarge holes with decent speed concentrically.
The finish on the vertical surfaces needs to bee pretty good as these are a tight fit but the bridging and support areas can be a little messy without too much ill effect.
They have a 1/2inch shank about an inch long.