Nuts are parts that closely connect mechanical equipment. Nuts and bolts of the same specification can only be connected together through the inner thread. For example, M4-P0.7 nuts can only be connected with M4-P0.7 series bolts (in nuts, M4 refers to the inner diameter of the nut is about 4mm, and 0.7 refers to the distance between two threads is 0.7mm); American products are the same. For example, 1/4-20 nut can only be matched with 1/4-20 screw (1/4 refers to the inner diameter of the nut is about 0.25 inch, and 20 refers to 20 teeth in each inch).