Generally speaking, the screw does not mean fasteners, generally used for transmission. A few times the "screw" can specifically refer to the threaded part of the bolt / screw.
 
Screws, fastener, are collectively referred to as fasteners or standard parts, screws including screws, bolts and studs.
 
What is the difference between bolts and screws?
Studs, a type of fastener that has no head and only two ends with external threads, such as double end studs, welding studs, and the like. (Sometimes called the screw, personally considered inappropriate).
 
What is the difference between a bolt and a screw?
The difference between screws and bolts and screws is minimal and is often confused, and there is no particularly clear specification line, but the screws are too small. Such as: self-tapping screws, set screws, wood screws and so on. Larger screws are called bolts, such as hex bolts, swivel bolts, carriage bolts, and so on.
 
 
 
But in general, bolts are used to connect two objects, usually through the light hole, need to use with the nut, a single connection can not afford. Tools are generally wrenches. Head mostly hexagonal head, generally larger.
 
How much wrench is the size of the screw
Screws usually do not need nuts, directly with the two objects to match (the general connector first drilling, tapping), the tool generally with a screwdriver (screwdriver), the head is mostly word slot, cross slot, inside and outside the hexagonal also a lot, Generally smaller.