01
Methods of indicating bolt specifications
M represents metric thread, and the major diameter of the thread is 14 mm, such as M14. Bolt specification M14, where M represents metric thread, means that the major diameter of the thread of the bolt is 14 mm. A complete thread mark usually consists of multiple parts, including thread feature code, size code, tolerance zone code, and other related information and standard code. For domestic screws, the national standard code is also added for identification.
△ Metric thread identification
Metric thread identification, the meaning of the major diameter of the thread is as follows. The thread feature code is represented by the letter "M". The size code varies depending on the thread type. The size code of single-line thread is "nominal diameter × pitch", and the pitch item can be omitted for coarse thread. The size code of multi-line thread is "nominal diameter × Ph lead P pitch".
△ Tolerance zone and screw-in length
The tolerance zone code consists of numbers and letters, with uppercase for internal threads and lowercase for external threads, such as 7H, 6g, etc. Note that these codes represent thread tolerances, not cylindrical tolerances. The screw-in length is divided into short, medium, and long. Generally, the medium length is assumed when not marked. If necessary, the screw-in length code S or L can be added, such as "M20-5g6g-L". In special cases, the screw-in length value can be specified, such as "M20-5g6g-30".
△ Direction of rotation and examples
Left-hand threads need to be marked with "LH" after the screw-in length. The screw-in length code and the direction of rotation code are separated by "-", and the right-hand thread is omitted. Marking example: M 16-5g6g indicates a coarse pitch ordinary thread, with a nominal diameter of 16, right-handed, and tolerance zones of 5g and 6g for the middle and major diameters; M16×1 LH-6G indicates a fine pitch ordinary thread, with a nominal diameter of 16, a pitch of 1, a left-handed, and tolerance zones of 6G for the middle and major diameters.
02
Bolt model and purchase guide
Involving diameter, pitch, and length, such as M81.2550. The bolt model is represented as: M-circular diameter × length (unit: cm), where M represents metric thread. For example, M81.2550 represents a bolt with a nominal diameter of 8mm, a pitch of 1.25mm, and a screw length of 50mm. L represents the bolt length, and D represents the nominal diameter.
△ Purchase suggestions
If you are not sure, it is recommended to purchase with samples. When purchasing screws, if you are not sure about the required model, you can purchase with samples or refer to the above representation method for selection. At the same time, being familiar with the standards is conducive to correct selection. Understanding the standards and representation methods of different bolt specifications is crucial for the correct selection and use of screws.