Early Omas and Minerva pens in celluloid are remarkably similar to Parker Duofolds. 

In his early years of activity Mr. Simoni repaired movie cameras and manufactured ebonite spare parts for Parker fountain pens. This made him very familiar with Duofold sizes and proportions and he implemented this experience manufacturing his own pens.

In many cases caps and parts of  Duofold-style Omas and Minerva pens are interchangeable with Parker pens.

This small Minerva pen is a very nice example of these similarities, which may not appear immediately evident because the pen is a ring top but it is has the same size as a Parker Vest Pocket Duofold pen.

The nib is very smooth and extremely pleasant to use.

These small Minerva pens are not very common.