Maybe I've missed something but I'm familiar with J pens (and predecessors), Safari's, M2's (which I just saw a 1960 ad which called them "new"), and a few other oddities, but I don't remember the K pens.
From 1956 ad.
Is this really a CX-100? It looks like the cap screws on. But the clip is too short.
Edited by AAAndrew, 09 April 2018 - 20:53.