lead of Thread
The distance a screw thread advances axially in one complete turn. On a single start tap the lead and pitch are identical. In a multiple start tap the lead is the multiple of the pitch
The diameter of the major cylinder or cone, at a given position on the axis that bounds the roots an external thread of the crests of an internal thread
The diameter of the minor cylinder or cone, at a given position on the axis that bounds the roots an external thread of the crests of an internal thread
The diameter of an imaginary cylinder or cone, at a given point on the axis, of such a diameter and location of its axis that its surface would pass through the thread in such a manner as to make the thread ridge and the thread groove equal and, therefore, is located equidistant between the sharp major and minor cylinders or cones of a given thread form. On a theoretically perfect thread, these widths are equal to one half of the basic pitch (measured parallel to the axis.) See illustration below.
tap with 3 to 5 chamfered threads.
The angular fluting in the cutting face of the land at the chamfered end. It is formed at an angle with respect to the tap axis of opposite hand to that of rotation. Its length is usually greater than the chamfer length and its angle with respect to the tap axis is usually great enough to direct the chips ahead of the tap. The tap may or may not have longitudinal lines.
A tap having a chamfer length of 7 to 10 threads