Went last night to the house of a friend of my wife's to service the pendant pen I call L'il Pudge. The refill had run out prematurely and the one I sent to replace it she said didn't fit. That didn't make sense to me so I went to visit the pen.
Long story short. I got there to find out that you can seat the refills into the screw tops at different depths and I had, indeed, done just that. So while I sat a made up a new refill she saw my pen case and purchased the other pendant pen I had with me as well. Not a bad deal!!
By the way, I find that the friction fit for the pendant refills doesn't stay well and the refill drops out the end of the pen as you walk around. What I do to fix this is fit the screw top and the refill together and then use a needle point punch to indent where they meet thus locking them together without taking anything out of round. It takes some patience though as the assembly likes to turn.