Main geometric parameters of self-tapping and self-drilling threads:
(1) Large diameter/tooth outer diameter (d1), which is the diameter of the imaginary cylinder where the thread crests coincide. The large diameter of the thread basically represents the nominal diameter of the thread size.
(2), small diameter / bottom diameter (d2): the diameter of the imaginary cylinder that coincides with the thread bottom.
(3), tooth distance (p): the axial distance of two points corresponding to the adjacent teeth on the meridian. In the inch system, the tooth pitch is indicated by the number of teeth per inch (25.4 mm).
The thread used on the double-head thread (GB897～900-88) is generally a common thread of coarse teeth. It can also be used as a normal thread or a transitional thread according to the requirements (according to GB1167).
Isometric double studs - Class B, can be made of 30Cr, 40Cr, 30CrMnSi, 35CrMoA, 40MnA or 40B as required, the performance of which is agreed by the supplier and the buyer.
The chemical composition of the material of the welded stud shall be in accordance with GB30981.1, but its maximum carbon content shall not exceed 0.20%, and shall not be made of free-cutting steel.
