I bought a Waterman Panta some time ago. It’s one of the first multi-function pens ever made. It was made in the fifties and sixties.
What I did not know when I bought it was that the refill, called "Pantabille," is no longer made. You can still buy some at ridiculously high prices in England, but even if you are will to pay the price, they have only black ones left at this time.
The refills have a slightly greater diameter and a shorter than the standard D1 refills for multi-function pens (5 4/8’’ rather than 5 5/8 ‘’). I found that Pentel BKSS7 (made for the four-color “Rolly”) are the right thickness and can be cut to size. The process is a bit messy, however, as the ink leaks after you have cut the refill to size. Scooping out a little ink, inserting a toothpick as far as it will fit, and breaking it off will fix it. But you have to be prepared to get your hands dirty.
As it turns out, standard D1 also work—and better. You need to cut off 1/8 of inch, which is easy with a razor saw or even a sharp utility knife (you just have to score it and then break it off). Ink is not a problem as these things are not even close to being filled to the top . Makes you wonder what you really pay for!)
The thickness is easily adjusted by electrical tape or even a bit of Scotch tape. (You don’t need to the whole thing, but only the part where clamping mechanism closes down). Works like a charm.
I like the look and feel of my Panta 3.