More suitable for processing non-ferrous metal extrusion tap, and tap the cutting works different, it is the metal extrusion, plastic deformation so as to form an internal thread. Threaded metal fiber extrusion is continuous, tensile strength, shear strength to teach high surface roughness processing also teach, but higher extrusion tap bottom outlet requirements: too big, base metals less, resulting in the Thread Trail is too large, the strength is not enough. Too small, enclosed extruded metal nowhere to go, causing broken tap. The calculation is: the prepared hole diameter = nominal diameter of -0.5 internal thread pitch.