Left to itself, this one will run for ever!
When Whitworth sat down in the 1840s and devised a standard for "threaded fasteners", his main aim was to make the things interchangeable, so that Joe the village blacksmith could go down to his B&Q (or whatever they had then) and buy some "threaded fasteners" which he knew would fit the Squire's traction engine when it came in for repairs. Whether he called them bolts or screws is immaterial and academic - he knew what he wanted and his only concern was that they would fit the job in hand.
Over the years other standards and designs have come along. Metric, ISO, Unified and many more. The hexagon head has been joined by slotted, cross-head, Allen and no end of others. Definitions have come and gone too, and common usage has blurred what was probably once an easily-described item of hardware. For instace, all bolts have screw threads. You screw a nut onto a bolt.
Whatever definition we now use for "threaded fasteners", someone will come up with an exception to prove it wrong. It makes for an entertaining discussion on the forum, but in the end we are just like Joe the blacksmith - we know what we need for the job, and as long as what we get fits, it really doesn't matter what its called.
Rick