Well that's funny,
Here in Europe bolts and screws are defined differently:
A bolt is something where you have to put something around it to turn it . Independently if there's a nut on there!
A screw is something where you have to insert a tool into to make it spin.
I think (I checked 2 things) that BMW in the repair manual uses the same system: The carb "idle screw" requires a flat blade screwdriver inside it.
"Head bolts' require a 6 sided spanner around them.
Both screws and bolts can have self tapping style threads for wood, concrete or metal. They can also have metric threads like the standards listed from Bolt depot above.
hope this helps.