The special tap for cutting oversized threads for screw thread insert is also called “ST tap”. Its large, medium and small diameters are one circle larger than the normal standard tap. For example, the major diameter of the standard tap M8 tap is 8.0mm, and the major diameter of the screw thread insert tap is 9.62mm. The larger circle is the space for installing the screw thread, forms a standard threaded bottom hole.
Marking method of STI taps: ST d (pitch) x p (nominal diameter)
For example, the diameter of the internal thread formed after the installation of the screw thread insert (or the diameter of the bolt that matches it) is 8mm, and the thread tap with a pitch of 1.25mm (ie M8) is marked as ST8x1.25
CRONAMETAL produces two kinds of STI straight tap and STI spiral taps in accordance with the national standard GB3464-83 and other standards, it can be used by a machine or by hand.