Fasteners refer to various screws, nuts, bolts, screws, etc. used to connect and fix parts in mechanical equipment and structures. In mechanical design and manufacturing, the selection of specifications and sizes of fasteners is very important, and they are directly related to the performance and safety of mechanical equipment and structures. Below, maijin will take bolts as an example to introduce how to calculate and select the specifications and sizes of fasteners. First, determine the type of bolts to be used. Bolts generally include ordinary bolts, high-strength bolts and stainless steel bolts, etc. Different types of bolts have different materials and strength grades, and the selection should be made according to specific conditions. Next, calculate the size of the required bolts. The size of the bolt mainly includes diameter, thread length, bolt length, etc. The diameter of the bolt refers to the diameter of the bolt thread, which usually needs to meet the requirements of bearing capacity, shear force, crack resistance, and bending resistance. The thread length of the bolt refers to the length that can accept thread failure before the bolt is cut off, generally not less than 2.5 times the thread diameter. The length of the bolt is determined according to the thickness to be connected and the assembly requirements. Then, make a selection based on the desired bolt size. Bolt dimensions include diameter, length, and surface treatment, among others. The diameter is generally available in standard sizes, such as M6, M8, M10, etc., and the appropriate diameter is selected according to the force to be carried. The length is selected according to the thickness to be connected. Generally, a certain length of bolts should be reserved for exposure, which is convenient for applying anti-rust agent and tightening. Surface treatment can choose galvanized, plastic spraying, hot-dip galvanized and other methods to improve the anti-corrosion performance of bolts. Then, check calculation and inspection of fasteners. After selecting the fasteners, some necessary calculations and inspections are required to ensure that they meet the requirements for use. The content of the checking calculation includes the bearing capacity, shear force, shear surface pressure, etc. of the bolts, which need to be selected according to the load conditions of the connected parts and the use environment. The content of inspection generally includes visual inspection, dimensional inspection, material identification, etc., in order to ensure the quality and reliability of fasteners. In general, the specification and size of the selected fasteners need to be determined according to the performance of the parts to be connected and the use environment, and also refer to relevant standards and specifications. During the selection process, factors such as bearing capacity, shear force and connection safety should be fully considered, and necessary checks and inspections should be carried out. The selection of fasteners has an important impact on the performance and safety of mechanical equipment and structures, so it should be given sufficient attention.