They are REALLY GREAT !!!! . (They fit only the Vertex click pen) . There seem to be no supplied instructions.
1) Remove the original nib section, ballpoint refill, and spring from the assembled pen
2) From the conversion kit package, take out the new nib section and the lead-holder mechanism
3) Insert the point of the lead-holder mechanism into the large top hole of the new nib section
4) Screw the mechanism into the nib section until the mechanism tip protrudes the right amount
5) Screw this assembly onto the previously assembled pen body
6) Click the top button until the lead protrudes for writing
Obvious as all this may seem, at first I forgot step (4). Then on close inspection I noticed the threads near the tip of the lead-holder mechanism and mating threads just inside the small hole of the new nib section.