Octagonal 4 J
These octagonal shaped safeties date back to the mid-1920s. Catalogues from that time marketed it as "elegant Achtkantform (octagonal shape); for those looking for a particularly elegant and shapely pen".
But, this particular model is rather special. The "J" imprint on the barrel means it was made to house a J-model calligraphic flexible nib. Notice the line variation promised by this nib in the 1932 price list picture. These nibs were made in size 2, 4, and 6, and are considered very rare and collectable today.
This pen is from the personal collection of Ariel Zuñiga - a generous contributor on FPN, seminal Montblanc collector’s books, and now this website. Watch out for a series of reviews of truly rare pens thanks to AZ’s generosity!
1932 pricelist: J nibs in sizes 2 to 6
The "J" imprint in the same orientation and font was also used by other pen manufacturers. Here is a picture of a Waterman from the 1920s with a similar font and orientation "J" imprint on its nib. Also, see this Edward Todd nib on David N.'s blog (link).
Photo credit: Christof C.M.Z. on flickr (link)
Safety fillers are a wonderfully intelligent filling system if you ask me. The nib unit rests inside the barrel when the pen is capped. After uncapping, a turning knob at the bottom of the pen is used to extend the nib unit and lock its collar against the section so that no ink can flow out of the barrel. Because of the fact that the nib unit is always submerged in ink, this pen was advertised as never suffering from hard starts!
For bibliography, see Resources page -->link