Pure guess
I would guess, after being on the forum for about 5 years, it was less of a pure guess, more like ‘quite clearly’.🙂
Made by someone with a bit of down-to-earth practical flair, I expect. Likely cost a few d, so even cheap back before 1971, and just as cheap since (in p’s).🙂
Last (only) one I made was a hefty lump of scrap drilled to size, slit and bolted to grip the work and a bolt through t’other end for the drive pin. Long gone in the scrap bin after using the one time.
I now have a drive plate so only need to use something like a nut-splitter (without the anvil, of course, or a heavy duty lifting eye). Seen both of those used by a friend…