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34 The geometric basis of the thread is a helix. The thread line is the hypotenuse of the triangle OAB to screw on the cylinder. Here d =d1 is the dividing diameter of the thread on the worm. Respectively, πd is the length of the dividing circle. Figure 2. The geometric basis of the worm Lead (ph). It is the linear distance through which a point on a thread moves ahead in one revolution of the worm. For single start threads, lead equals the axial pitch, but for multiple start threads, lead equals the product of axial pitch and number of starts. Mathematically: ph = p z1 (3) where p = Axial pitch; and z1 = Number of starts. Lead angle. It is the angle between the helix on the pitch cylinder and the plane normal to the axis of the worm. It is denoted by γ. From the geometry of the figure, we find that tg γ = ph/( πd1) = pz1/( πd1) = πmz1/( πd1)= mz1/ d1 (4) where p is the thread pitch; d1 is the dividing diameter of the thread, γ is the elevation angle of the helical line (Lead angle), z1 is the number of starts. From the equation, you can determine the dividing (pitch) diame-ter of the worm: qmzmdtg11. (5) where q is the coefficient of the worm diameter. Coefficient of the worm diameter q = z1 / tgγ (6) q is standardized and associated with the module as per GOST 2144 - 76.