Apr 00 - Heli-Coil STI Gages vs. Generic STI Gages

Heli-Coil STI Gages vs. Generic STI Gages

One of the reasons users of Heli-Coil Thread Inserts find our products so consistently reliable is that we offer what we refer to as the "complete system". This includes all aspects of the Heli-Coil assembly process from hole preparation to finished thread. This includes taps, gages, inserts, installation tools, and tang removal tools. Each component of the system is designed to work together. One of the most important of these is the Heli-Coil STI Thread Gage.

Heli-Coil Thread Inserts are manufactured to such tight tolerance (+/- .0001") that the accuracy of the finished hole is solely dependent on the accuracy of the tapped hole (Ref. MS 33537, MA 1567). If the STI tapped hole gages correctly, then the finished hole with the insert installed will be within specification. This makes the tapped hole and the gage itself an integral part of the process.

If hole preparation is performed under the appropriate MS or MA specification, you are instructed to gage the tapped hole prior to installing the insert. Because the tolerances are critical for an accurate assembly, Heli-Coil STI gages are designed to both "w" and "x" tolerance ranges. The "w" tolerance is more restrictive and is generally reserved for the smaller thread sizes where the tolerances are more critical. For these small thread sizes, the gage should be specifically identified as an STI thread gage manufactured to "w" tolerance standards. Most non-Heli-Coil brand gages are manufactured to "x" tolerances. This tolerance band is wider than the "w" band and therefore less costly to produce. However, this tolerance band, when used in small thread size applications, may not always allow for the correct fit relationship for the insert assembly.

For further technical assistance, please contact the Applications Engineering Group.

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