The ends are simply a cut off end of all thread. In fact, on closer inspection, it looks like the threaded portion isn’t original to the tool. The threaded portion is sunk into a bored cap that’s been cross drilled. While the shoulder bolt holds the whole thing together, and provides a way to turn the screw. Sorry everyone, but it looks like these are modified for someone’s purpose, and that guy is long gone. Thanks for your efforts though.