Square nut is a nut, bolt or screw fastening screw together to play the role of parts, an original all manufacturing machinery must be used. Quartet nut is tight mechanical equipment, spare parts close connected by threads inside, the same size and screw the cap nut can be connected together. Many types of nuts, our common national standard, British standard, American Standard, the subject nut nut according to the different materials, divided into carbon steel, high strength steel, stainless steel, steel and other major types correspond to different countries depending on the product properties Standard is divided into ordinary, non-standard, (old) GB, the new national standard, American, British, German standard. Of different sizes, ranging from the thread into different sizes