I saw jbr something or others 3 part video on making kitless pens. Searching for the taps and die sets they seem to be pretty expensive on the Turner's based websites. 180 ish for the m13 x1. I found a m13x 1 on Amazon for 30 bucks. Am I missing something??
In addition to what Pete said, there are other differences ... as well as often being triple start, the threading for pens is usually ...
of a finer pitch, and a shallower thread depth (which goes with the finer pitch).
There is nothing to say you can't do your own thing, but pen making has its own constraints which you have to take into account. . One of these constraints is that pen barrels and caps are cylindrical, and the wall thickness of these cylinders requires that you choose threads that don't critically weaken the walls.
The m13 x 1 thread size that you mention has a pitch, as you would know, of 1 mm. . The die/tap that cut such threads would make the depth of the thread approximately 0.75 mm or 0.8 mm (there is a rule of thumb for the relationship between pitch and depth, but I just can't remember that rule at the moment). . That depth of cut would require that you keep the cylinder wall thickness at about 2mm or so. . A typical pen-makers tap/die for m13, would have a pitch of 0.75 mm or 0.8 mm. . The depth of cut would be roughly 0.6 mm. . The pen-makers tap/die would be, as Pete said, more expensive because of the specialty market.