Well, I can't say for sure, but I can make an educated guess. It's not beyond reason for him to have just sized everything to be the appropreate size for the different fits. What I mean is, the blank would be bored out to be a press fit for the nib, so instead of doing a 10mm bore (or what ever size tube that nib normally fits) he would either make the bore the size of the tubes ID, or simply figure out the appropriate size for the bore by looking up the size difference needed for a press fit (a machinest handbook has this information). The same would be done for the cap, but a looser fit and the end would be threaded. It's not beyond reason to do this, but you would need a metal lathe to get some of the sizes with in the tolerence (only a few thousandths of an inch, if memory serves) as well as make the threads. As I said, I don't know this for a fact, but don't see why that wouldn't work.
NAH
