Three vintage trifold Filofaxes for comparison

These all have different ring sizes. The most compact is the D2CLF1/2 (bottom), which is in the narrow form of duplex (two sets of rings) where the pages overlap when open. The D2CLF7/8 (top) is in the wide duplex form. And the 10CLFJ5/4 (right) is the rather splendid, conventionally ringed variety with the built-in jotta.

Done