The 55X series of piston fillers was introduced by Omas at the end ot the 1940's.
It comprised cylindrical and facetted models in three sizes: 555, 556 and 557. Facetted models were identified with the letter F following the model number.
This line of pens was extremely successful and remained in production till the 1960's. All the models were highly reliable everyday users and had very beautiful 14 ct nibs.
The facetted line was fitted with Omas Extra Lucens nibs, exactly like the ones Omas had used in the 1930's for the top line of the Extra lucens pens, while cylindrical pens had Omas Extra nibs.
This Omas 556/F is fitted with a very pleasant EF Extra Lucens nib, which is smooth and very flexible,