Studs: consisting of the head and the screw (with the external thread cylindrical) sections of a type fasteners, to be with the nut for fastening two parts with hole. This connection type called bolt connection. As to unscrew the nuts from the bolts, but also so that the two parts separately, it is part of removable bolted connection. General classification and special bolt connected by force and have sub-normal articulation hole of. Force major general carry axial and lateral forces also carry less demanding. Articulation hole bolt and hole size to fit in time by using lateral force. Divided by the head shape hexagonal head, round, square head, countersunk head and so on. Wherein the hexagonal head is the most commonly used. Shen head with a general requirement in place after the connection is not smooth surface projections, because countersunk head can be screwed into the part in. Round to be screwed into parts inside. Tighten the square head of the force can be bigger, but large in size. In addition, to meet the needs of the installation lock, there is a hole in the head, the shank has a hole, the holes can not to release the bolt when subject to vibration. Some did not bolt threaded rod to be meticulous, called the waist bolts. This bolt is conducive to change by force the coupling. There are special high strength bolts, the head will enlarge some, there are changes in the size of the steel structure. Another special use of: T-shaped slot bolts, used on jigs most special shape, side of the head to be cut off. Bolt, and ground connection for machine fixed, there are a variety of shapes. U-bolts, as described above. And so on. There are special stud welding, one did not have a head screw, you can weld on the part, tighten the nut on the other side directly. Steel bolt performance levels meaning bolted performance rating 3.6,4.6,4.8,5.6,6.8,8.8,9.8,10.9,12.9 more than 10 levels, of which more than 8.8 and bolts made of carbon steel or in carbon steel and heat treatment (quenching and tempering), commonly known as high strength bolts, the rest is known as ordinary bolts. Bolt performance rating label has two part numbers, respectively, said male bolt material tensile strength and yield strength ratio. For example: performance level 4.6 bolts, its meaning is: 1, bolt material nominal tensile strength of 400MPa grade; 2, bolt material yield strength ratio of 0.6; 3, bolt nominal material yield strength of 400 × 0.6 = 240MPa performance level grade 10.9 high strength bolts, the material after heat treatment, can be achieved: 1, bolt material nominal tensile strength of 1000MPa grade; 2, bolt material yield strength ratio is 0.9; 3, bolt nominal material yield strength of 1000 × 0.9 = 900MPa Stud performance rating is the meaning of international standard, the same performance level of a bolt, regardless of the origin of the difference between the material and its performance is the same, the design performance levels can use only. Strength class called 8.8 and 10.9 refer bolts shear stress level is 8.8GPa and 10.9GPa 8.8 nominal tensile strength 800N / MM2 nominal yield strength of 640N / MM2 general bolt is "XY" indicates the intensity, X is * 100 = This bolt tensile strength, X * 100 * (Y / 10) = This bolt yield strength (because of the identification requirements: yield strength / tensile strength = Y / 10), such as 4.8, then the bolt tensile strength: 400MPa, yield strength: 400 * 8/10 = 320MPa