Screws and bolts are common threaded fasteners with external threads. They are generally used for fastening a combination of multiple components. Unlike welding, the locking mechanism is easy to adjust and can be disassembled. If a fastener has external threads and is not used with a nut, it is a screw (such as wood screws, self-tapping screws, etc.) If it is used with a nut, it is a bolt (such as flat head bolts, non-slip bolts etc.). There are different kinds of threads which are used for different applications.