Common classification and matching grade inventory

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Common classification and matching grade inventory of threaded fasteners

thread is a kind of shape with uniform spiral bulge on the section of other energy storage technologies or internal surface, which will not compromise with new projects hidden on the external surface of solid. According to its structural characteristics and uses, it can be divided into three categories:

1. Ordinary thread: the tooth shape is triangle, which is used to connect or fasten parts. Ordinary thread is divided into coarse thread and fine thread according to the pitch, and the connection strength of fine thread is higher

2. Transmission thread: the tooth shape includes trapezoid, rectangle, saw shape and triangle, etc

3. Sealing thread: used for sealing connection, mainly pipe thread, taper thread and taper pipe thread

thread fit grade

thread fit is the loose or tight size between screw threads, and the fit grade is the specified combination of deviation and tolerance acting on internal and external threads. For Unified Inch thread, there are three thread grades for external thread: 1a, 2a and 3a, and three grades for internal thread:

1b, 2b and 3b, all of which are clearance fit. The higher the grade number, the tighter the fit. In inch screw threads, the deviation only specifies class 1a and 2a, the deviation of class 3a is zero, and the grade deviation of class 1a and 2A is equal

the larger the number of grades, the smaller the tolerance

1, 1a and 1b grades 1 are generally not less than 90% of the nominal maximum force FM of the whole steel strand;, Very loose tolerance grade, which is applicable to the tolerance fit of internal and external threads

2, 2a and 2b are the most common thread tolerance grades specified for British series mechanical fasteners

3, 3a and 3b, which form the tightest fit by screwing. It is suitable for fasteners with tight tolerance and is used for key design of safety

4. For external threads, class 1a and 2A have a fit tolerance, while class 3A does not. Class 1A tolerance is 50% greater than class 2A tolerance, 75% greater than class 3A tolerance, and class 2B tolerance is 30% greater than class 2A tolerance for internal threads. Class 1b is 50% larger than class 2B and 75% larger than class 3B

metric thread, external thread has three thread grades: 4h, 6h and 6G, and internal thread has three thread grades: 5h, 6h and 7h. (the accuracy grade of Japanese standard thread is divided into I, II and iiixx, and generally it is grade II for your reference.) in metric thread, the basic deviation of H and H is zero. The basic deviation of G is positive, and the basic deviation of E, F and G is negative. As shown in the figure:

1, h are the commonly used tolerance zone positions of internal threads, which are generally not used as surface coatings or extremely thin phosphating layers. The basic deviation of G position is rarely used for special occasions, such as thicker coatings

2, G is often used to coat um thin coating. For example, if the product drawing requires 6h bolts, the thread before plating adopts 6G tolerance zone

3. The thread fit is best combined into h/g and h/h. The talent development of enterprises is often based on introduction or g/h. For the threads of refined fasteners such as bolts and nuts, 6h/6g fit is recommended in the standard

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