A thread is a shape having a uniform spiral protrusion on a section of the outer or inner surface of the solid. According to its structural characteristics and uses, it can be divided into three categories:
1.Ordinary thread: The tooth shape is a triangle for connecting or fastening parts. Ordinary threads are divided into coarse teeth and fine thread according to the pitch, and the connection strength of the fine thread is high.
2.Transmission thread: The tooth shape has a trapezoidal shape, a rectangular shape, a saw shape and a triangular shape.
3. Sealing thread: used for sealing connection, mainly for threading, taper thread and taper pipe thread.
External thread has three thread grades: 4h, 6h and 6g
Internal threads are available in three thread sizes: 5H, 6 H, 7H. (Japanese standard thread accuracy grade is divided into three levels I, II, III, under normal conditions is level II)
In metric threads, 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.
1.H is the common tolerance zone position for internal threads. It is generally not used as a surface coating or an extremely thin phosphating layer. The basic deviation of the G position is used for special occasions, such as thicker coatings, which are rarely used.
2.g is usually used to plate 6-9um thin coating, such as the product drawing requirements of 6h bolts, the pre-plated thread uses a 6g tolerance zone.
3. The thread fit is best combined into H/g, H/h or G/h. For the refined fastener threads such as bolts and nuts, the standard is recommended to use 6H/6g.