TL;DR: In the 1970s, Sailor made its Mini line with 21k-gold nibs. Better, they equipped these pocket pens with various nibs, of which the Zoom is the nib that produces different strokes depending on the writing angle: Hold the pen higher, closer to the vertical, and it writer thinner; hold the pen closer to the ideal hold at 45- to 50-degrees, and it writes thicker. Here is such a Sailor Mini 21 with Zoom nib.