Thanks a lot for you inputs, Jim, Kronckew and 'Nando,
I was sent this image about two years ago by an East German antiquarian book deealer (
sedulitas) and they assured me that both the ball and chain illustrated were a half ball from a chain shot, and they were not willing to sell it. They regarded it as kind of permanent historical decorative basis for advertisimg their old mss. So that's all I can telly you, folks, sorry though I am.
Best,
Michael