It is not a Safety, but a Montblanc Lever Filler model No. 4, produced between 1922 and 1929. With the Safety, the nib is extended and retracted via a turning knob at the barrel end; with the lever filler, the lateral lever presses via a small plate on a rubber sac. It is not a Meisterstück, since this series carries 18-carat nibs and the cap engraving "Meisterstück" or "Masterpiece" as well as model numbers from the 20/25-45 range. A detailed description can be found in the book "Fountain Pens of the World" on page VII of the appendix.