The famous green striped version of this well known pen. The 400NN entered production on April 23, 1956 and ran until July 28, 1965. It completed the transformation that the 400N had begun. Instead of a flattened dome, the cap top became more pointed and integrated into the cap itself. The crown nut holding the clip in place is also thinner than what was employed on the 400 and 400N. The cap is somewhat longer than that of the 400N though it retains a similarly shaped beak clip. The piston knob on this version is longer and more pointed than the preceding models.(https://thepelikansperch.com/2019/03/05/pelikan-400-fountain-pen/) Good working condition.