How to express bolt specifications and understand bolt specification descriptions

TIME：

2021-11-09

Bolt specification representation method:

Bolt specification M14 represents a metric bolt with a thread diameter of 14mm. M represents "metric, metric" thread. The complete thread marking is composed of: thread feature code + size code + tolerance zone code + other information + standard code (such as: adding national standard code to domestic screws)

1. The thread feature code is the letter "M"

2. Size code The size code of single-line thread is "nominal diameter × pitch". For coarse thread, the pitch item can be omitted. The size code of multi-line thread is "nominal diameter × Ph lead P pitch".

3. The tolerance zone code is represented by numbers and letters (uppercase letters for internal threads and lowercase letters for external threads), such as 7H, 6g, etc. It should be noted that 7H, 6g, etc. represent thread tolerances, while H7, g6 represent cylindrical tolerance codes.

4. The screwing length is specified as short (indicated by S), medium (indicated by N), and long (indicated by L). In general, the screwing length of the thread is not marked, and the thread tolerance zone is determined according to the medium screwing length (N). If necessary, the screwing length code S or L can be added, such as "M20-5g6g-L". When necessary, the value of the screwing length can be indicated, such as "M20-5g6g-30".

5. The left-hand thread should be marked with "LH" after the screwing length. The screwing length code and the rotation direction code are separated by "-", and the right-hand thread is omitted.

6. Marking example: M 16-5g6g indicates coarse thread, nominal diameter 16, right-handed, thread tolerance zone middle diameter 5g, major diameter 6g, screw length is considered medium length. M16×1 LH-6G indicates fine thread, nominal diameter 16, pitch 1, left-handed, thread tolerance zone middle diameter and major diameter are both 6G, screw length is considered medium length. Most screws do not have any model number marked on the surface. If you do not know the model number of the screw you want to buy, you can buy it with a sample. The model number of the bolt is expressed as follows: M-circular diameter*length (CM), that is, M-number. M represents metric thread. For example, M8*1.25*50 means the nominal diameter is 8mm, the pitch is 1.25, and the screw length is 50mm; L represents the length of the bolt, and D represents the nominal diameter.

Specification standard - GB standard Square head bolt Grade C GB 8-88 Countersunk head square neck bolt GB 10-88 Countersunk head tenon bolt GB 11-88 Semi-round head square neck bolt GB 12-88 The above is an introduction to the bolt specification representation method and how to read the bolt specification model. I believe that you will have more understanding after reading it. The content is for your reference only. I hope it can be helpful to you.

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