Nuts are nuts, which are screwed together with bolts or bolts to tighten the parts. All manufacturing machinery must use one kind of original parts. Nuts are of various kinds. We often have nuts of national standard, British standard, American standard and Japanese standard. Nuts are divided into carbon steel, high strength, stainless steel, plastic steel and other major types according to different materials. According to product attributes, they correspond to different national standard grades. For ordinary, non-standard, (old) national standard, new national standard, American system, British system, German standard. Generally speaking, national standard and German standard are expressed by M (e.g. M8 and M16), American standard and British standard are expressed by fractions or (e.g. 8, 10, 1/4 and 3/8) fasteners. Nuts are parts that are closely connected with mechanical equipment. They can be joined together only through internal threads, nuts of the same specifications and screws. For example, M4-0.7 nuts can only be joined with M4-0.7 nuts. Rod matching (in nuts, the inner diameter of M4 finger nut is about 4 mm, the distance between 0.7 finger and two threaded teeth is 0.7 mm); the same is true for American products, such as 1/4-20 nut can only be matched with 1/4-20 nut (1/4 finger nut has an inner diameter of about 0.25 inches, 20 fingers have 20 teeth per inch).