Correct. Marklin had determined the feasibly 1:220 at 6.5mm was the smallest model train ratio when it came to detail and operation. The went with Z as it was the last letter of the alphabet.
Märklin did select that name to show all potential customers that this is the smallest scale you can get.
Ztrack Magazine Ltd.
Distributor for American Z Line
Full Throttle & Rokuhan
Authorized MTL, InterMountain
and Tenshodo dealer.
6142 Northcliff Blvd
Dublin OH 43016