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 many books, articles, technical papers, manuals and other sources. To understand them is a requirement 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 two thread sides, measured in an axial plane (along an axis)

• CREST (also see ROOT)

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

• DEPTH OF THREAD

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

• EXTERNAL THREAD

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

• INTERNAL THREAD

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

• HELIX ANGLE

  is the angle made by 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...