I think you have your registration distance wrong — the Zenit 3m registration distance was 45.2mm, not 17.35mm — I think you might mean that the registration distance is 17.35mm more than the more common m39 screw (aka Leica screw).
Thanks for pointing that out, Bob! I’ve verified (with a ruler) and updated the article.
bob.janes Apr 10, ‘23
Dmitri Apr 10, ‘23