will,
i suspect that the "10mm scale" refers to miniatures (wargamming).
20mm, if memory serves me, is roughly 1:72...
it is equated with HO, and some use it as such.
so then, 10mm would be 1:144, "close enough" for n scale.
(actually, i think some u.k. manufacturers use, or used, the 1:144...