First, the scope of application Second, the three-performance bolts, screws, anchor bolts and other externally threaded fasteners are marked with 307A, 307B and 307C respectively. Third, the material Fourth, the processing technology V. Mechanical properties 1. Hardness: The hardness of Class A and Class B bolts and studs is as specified in Table 4. The Class C anchor bolts have no hardness requirements. 2. Tensile strength (1) ASTM A307 and SAE J429: ASTM A307 Class A mechanical properties are basically the same as those in SAE J429; Grade B is basically the same as J429. ASTM A307 Class C is required to have a high degree of plasticity and must have an elongation of ≥23% after fracture, which is equivalent to 4.6 in ISO. (Note: The machined specimens of the US standard inch series are 4 times the diameter.) 3. Several principles (1) Principle 1: Bolts and studs with a nominal diameter of ≤11/2 in. When the length is allowed, the tensile test of the product shall be carried out. Bolts and studs with a nominal diameter of >1 1/2 in. should also be considered for the tensile test of the product. If the conditions are not allowed or due to the length of the product, the full-size physical tensile test cannot be performed, and the machined specimen shall be used for the tensile test. Sixth, product size and thread VII. Product Marking 1. Mark content: Class A - 307A; Class B - 307B; Class C - painted white at the end of the anchor bolt.
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(2) Tensile strength requirements: See Table 5 for the physical bolt and stud tensile load, and Table 6 for the tensile strength of bolt and stud machining samples. 
(2) Principle 2: If both the physical tensile test of the product and the tensile test of the machined sample are carried out, if the results of the two tests are inconsistent, the results of the physical test of the product shall be used as the basis for acceptance.
(3) Principle 3: If both hardness and tensile strength tests are carried out at the same time, and the hardness test results are lower than the standard value, the tensile strength test results should be used as the acceptance basis.
ASTM A307 standard is the mechanical properties of low carbon steel externally threaded fasteners. The product size should be in accordance with the corresponding product standards, as specified below: 
2. Marking method: The position of the mark is: the bolt is on the top surface of the head, the thread is at one end of the rod, and the anchor bolt is at the end of the rod. Studs and anchor bolts are only marked with a nominal diameter of ≥ 3/8 in.