Nuts are parts that tightly connect mechanical equipment. Through the threads on the inside, nuts and bolts of the same specification can be connected together. For example, M4-P0.7 nuts can only be connected with M4-P0.7 series bolts (in the nut Among them, M4 means that the inner diameter of the nut is about 4mm, and 0.7 means that the distance between the two threads is 0.7mm); the same is true for American products, for example, 1/4-20 nuts can only be matched with 1/4-20 screws ( 1/4 means that the inner diameter of the nut is approximately 0.25 inches, and 20 means that there are 20 teeth in every inch).