It is a rather strange language we speak isn't it, we SCREW bolts into things just the same way we screw woodscrews into things. If we use bolts, the thing is said to be BOLTED together and if using screws, is Screwed together. If we tend to use small 'bolts' for model engineering, we tend to call them screws but when the item is assembled, it is said to be BOLTED together.
The general trend with our language seems to imply anything with a woodscrew type thread is definately a screw. Anything with a machined thread is called a bolt.. unless it has a screwdriver slot in the top, in which case it becomes a screw!
I know this is not gospel and I don't speak as an expert by any means but this seems to be the general speak amongst most people when they request fastenerswith which to put things together.
As an aside, it is my guess that the first rotatable fastner would have been the screw and when a question was recently put about which invention has been the most significant in mankinds history, I dont remember anyone mentioning the humble screw (bolt). Without it, none of the engineering miracles would have been created and the whole world would have fallen apart.
Just my tuppence worth.
Chris