These two scales are the largest of the “small scales” before moving into “mid-size scales” with model railway’s O-gauge at 1:48 (39mm wargames scale equivalent).
1:66 is not a genuine model scale, it is a transposition of the 28mm wargames scale created by Games Workshop, and followed by many manufacturers through scale creepage from 25mm. For static-scale purists such as myself, it has been amusing to watch GW creep their own scales upwards, such that many of their supposed 28mm ranges are nicknamed as 32mm scale.
1:64 used to be a popular kit-modelling scale. It is also the ratio scale of railway modelling S-gauge scale, plus of the micro-Scalextric slot car racing system.
(page incomplete – more to follow
