根据我厂制造的梯型(α=30°)双线(头)螺纹,在制成后磨去一线故而形成一种“特殊螺纹”(图1)。对于该螺纹的螺距t,半角α/2的测量,基本上与普通螺纹测试方法相似,故省略。现着重谈该螺纹的中径测量,我们是采用三线量法。由于螺纹两相邻螺距较宽,螺纹螺旋升角较大,常用三线规格又不适用,以及螺旋升角公式等问题。 According to my factory-made ladder (α = 30 °) two-wire (head) thread, after grinding in a line so as to form a “special thread” (Figure 1). For the thread pitch t, ​​half-angle α / 2 measurement, basically similar to the general thread test method, it is omitted. Now talk about the diameter of the thread measurement, we are using the three-line method. As a result of the thread two adjacent pitch is wider, thread helix larger angle, commonly used three-wire specifications do not apply, and spiral angle formula and other issues.