What kind of screw thread is made of?

As long as there is industry on the planet, screws are indispensable in everyday life. We often contact such as the use of camera, glasses, watches, electronics and other small screws; TV, electrical products, instruments, furniture and other general screw; as for the engineering, construction, bridges use large screws, nuts, transportation equipment, aircraft, cars, automobile and other for screw size and use. Screws have an important task in the industry, the function of the screw is always important.
Copper screw lock once completed, drilling and tapping, strong binding force, save construction time, improve work efficiency. Copper screw accuracy usually 6G grade (grade 2, a U.S. - spec "IFI" 2A tooth), engineering construction with the crude screw 8g level (Level 3, the IFI for tooth 1a).
Copper screw thread is what kind of?
1 square thread (90 degrees) power transmission
2 trapezoidal thread (30 or 29): power transmission
3 V-thread (60 degrees): binding / locking
4 for triangle thread (55 degrees): binding / locking