That's funny. I've bought several machinist boxes, and never found one. One box was full of refrigerator magnets, another electrical stuff, an third electronic engineer tools, and 2 empties.
But I've never found one of those in any other box I've bought either, and that's 6 or 8 more.
I always had a small roller but not a screen spline roller. Mine was about an inch wide and it was used to seal stainless steel foil pouches used when heat treating air hardening tool steel.
I was a machinist over 20yrs, and while I have one, it was always at home, not in my machinist box.
While I did not go around looking in people's boxes, I don't recall ever seeing one in any drawer that happened to be open when I approached.
Father-in-law was a machinist/modelmaker in a prototype shop. Several spline tools in his toolbox. Wonder if they are useful for some "off-brand" purpose...
A cousin's stepfather was a US Steel millwright in the 1940s-'60s. When my cousin was going through his deceased stepfather's work tool box, in it was a .25 automatic pistol. The shop could be a rough place in those days.