Hi-Tech has produced more than ten thousand kinds of screws.
Screw is specially treated for aesthetic and identification purposes by color-coating or spray.
A plastic layer is attached onto the thread against slipping by increasing its friction and tightness.
It is usually made for specific application. As the threads of two sides can be different, the fastener possesses different screw thread on each side, it then provides the ability to fasten up two different material work pieces together.
Nut is an internally threaded which is commonly used opposite a mating bolt to fasten a stack of parts together.