So, what's the difference between a bolt and a screw?
George always pipes up when he hears me ask this... "Have ya ever been bolted?"
No, George, I can't say I have.
So what is the dif'?
Bolts hold the material and usually compress it.
Screws are held by the material and are usually compressed by it.
Bolts have / use nuts or some sort of a compatible threaded interface.
Screws are compression fit into or thru and held tight by a material like wood, metal, plastic or bone (perish the thought).
That's that. Pretty simple, eh?