And here’s the complete[1] Zento Signature 3 kit.
The mechanism uses the same center part and sliders (and I assume, springs) as other Uni 3-colour pens (the knurled ring is crimped to it so the thread on that part is unused). The selector is different, with a complicated profile to create half stops between refills. The hexagonal end clips to the selector and attaches the whole mechanism to the body. The magnetic ring covers the junction and makes it seem as if there’s only one part. As in the single colour Zento, the rear part is mostly plastic.
Well, almost: I didn’t remove the magnetic ring from the nose part and the magnet from the cap ↩︎