Threading is a relatively large subject, in fact, it is large enough to have a whole book dedicated to it. As subjects of this kind usually are, threading has its own technical terms. These terms appear in books, articles, technical papers, manuals and other sources. To understand them is mandatory for any CNC programmer and operator.

Listed here are some of the most common terms used for threads and thread cutting:

• ANGLE OF THREAD

  is the included angle between the sides of the thread, measured in an axial plane

• CREST

  is the top surface of a thread that joins the two sides

• DEPTH OF THREAD

  generally, the distance between the crest and the root of the thread, measured normal to the axis (in programming, depth is considered as a measurable value per thread side)

• EXTERNAL THREAD

• is a thread that is cut on the outside of the machined part, for example as a bolt

• INTERNAL THREAD

  is a thread that is cut on the inside of the machined part, for example as a nut

• HELIX ANGLE

  is the angle made by the helix of the thread at the pitch diameter with a plane perpendicular to the axis

• LEAD

  is the distance the threading tool will advance along an axis during one spindle revolution. The lead always determines the threading feedrate and can have constant or variable form.

• MAJOR DIAMETER

  is the...