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Gage STI Before or After Inserted

Should I test the STI threaded hole after the STI is inserted?

I get asked frequently: Should I gage the thread after the screw thread insert is installed?

The short answer is: No.

For a more detailed answer I refer you to page 24 or Emhart Teknologies' Heli-Coil Catalog # HC 2000 Rev 1 (02/05) 15M (In case you did not know, Emhart is the company that invented the Screw Thread Insert.):

Accuracy of the finished thread when the insert is installed is dependent upon the accuracy of the tapped hole. If the finished tapped hole gages satisfactorily, the installed insert will be within the thread tolerance. It is not necessary to gage the installed insert. After the insert is installed, the GO thread plug gage may not enter freely; however, the insert will always seat itself when the bolt or screw is installed and tightened.

What more needs to be said?

Here is a video on a brief history of the Helicoil Screw Thread Insert (STI):

Related Link:
STI Thread Gage Tolerances

This data is provided for general information only. The intention is to provide accurate information; regardless; errors may exist in the supplied information. If accuracy is critical, base your final decisions on the data provided in the root document: A-A-59158:1998; which is a copyrighted document. To purchase a copy visit an Authorized Reseller.

Original Posting: 9/25/2009
Last Revision: 2/18/2015
Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com.

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