The Snap Cap

[deepak23]

Of course not - I just haven't encountered any of those ones yet.

 

And of course not all sections are threaded - I was resaccing a Skyline about half an hour ago! When I was asking why threaded caps weren't a thing in the early days of fountain pens, but threaded sections were, I was referring to eyedroppers (straight and taper cap ones). They clearly had the ability to chase threads into hard rubber - why not do it on the caps, too?

Probably because that would result in a much thicker cap. See the handmade indian ebonite pens for reference. The caps are almost as thick at the threads as the barrel is at the section