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在螺纹的外径和底径之间,有一个假想的直径,叫做有效直径,又叫节径或平均直径。有效直径的测量,有直接测量法和间接测量法:直接测量法是用螺纹千分尺来测量,它的好处是操作简便,可以直接读出有效直径的数值;缺点是误差较大,精确度不高。因此,高精度的螺纹都要用间接的测量方法,就是三线测量法(又叫三针测量法)。
Between the thread’s outer diameter and bottom diameter, there is an imaginary diameter, called the effective diameter, also known as the pitch diameter or average diameter. The effective diameter measurement, direct measurement method and indirect measurement method: direct measurement method is to use a screw micrometer to measure, its advantage is easy to operate, you can directly read the effective diameter value; disadvantage is the error is large, the accuracy is not high . Therefore, high-precision threads are used indirect measurement method, that is, three-wire measurement method (also known as three-pin measurement method).