Ball End Strings
I'm glad we don't have twist our own
Virtually all steel guitar strings have an end that looks like this:
It's called a "ball end string" even though the ball is a cylinder, and usually hollow like this one. The ball either seats
under the top a guitar with a pin bridge, secured by a bridge pin, or pulls in from the backside of a pinless bridge, or is held by a tailpiece. Offhand, I can't think of any steel string guitar that's designed for anything but ball end strings.
Ball ends are sometimes fixed to banjo strings, and sometimes to nylon guitar strings, but they are hardly ever used on professional grade banjos or classical guitars.