Morris Minor Owners Club

Surely the difference is that a bolt has a linear shaft and a screw is tapered?

No,
As quoted by 57

Les is correct - even a hex. head bolt is a set screw once the thread extends to the head. It gets complicated and sometimes confusing!

The use differs when a bolt is used to bolt one piece to another while a set screw enables the parts to be bolted to each other by the fact that both parts are threaded hence both parts are screwed together.

"Lead screw" yes on a metal turning lathe?

Yes thats one application, also on milling machines ect and are designed for minimal backlash.
Screws are threaded from the head to the end, if it does not have a head it is called studding.

never underestimate the lead screw. our western civalisation is built on it

Have to disagree the Brixton the Bodgers Lathe was 1st.
And for those that dont know historically the Bodger was a skilled man unlike todays version

today were using lead screws to observe the most distant galaxies, very precise and fast using stepper motor. adaptive optics. they dont fail on saterlites, unlike hydraulic systems, its difficult to repair thing in space