The safety pens made by Montblanc were built in several sizes designated by numbers. The rarest size is probably held to be the Safety No. 12. Such a piece was to be seen both at the Cologne collectors' meeting in March 2004 and at the meeting in March 2005, on each occasion as a single, much-noticed example, and among collectors it is traded as a pronounced rarity.
Besides the size, the version determines the rarity. Octagonal body shapes and elaborate metal overlays are particularly sought after: an octagonal Safety No. 2 with a gold overlay was in 2005 among the pieces that attracted the greatest attention in Cologne. Anyone interested in safety pens will find such variants practically only at the large international collectors' meetings, where they are shown individually and mostly for one day only.