I still don’t get the difference b/t the one piece and two. But most stylus can take either one, is that correct?
From a practical point of view, there’s little difference between the two. Don’t worry about it.
The holder grips the shank, which is thick. The needle, which is thin, is inserted in the follicle. How you get from shank to needle is the difference between one piece and two piece.
In the one piece, it’s all one solid piece of metal.
In the two piece, the shank is a hollow tube; in maufacturing, the needle is inserted in the tube, which is then squeezed (crimped) to hold the needle in place.
F and K refer to shank diameters. F is thicker, I think. Because I like to do things the hard way, I use K shank tapered needles, which are hard to find.