STI Thread Guage use to gage the thread Before the Heli-Coil inserts is installed or after ?
hope anyone can help me with this , thank
If I understand the question correctly, a STI plug gage is used to test the thread prior to insertion of the heli-coil thread insert.
For example (taken from our gages):
1/4-28 UNF 2B STI plug gage has the members with a pitch diameters of .2732 (go) and .2765 (no-go)
1/4-28 UNF 2B plug gage has the members with a pitch diameters of .2268 (go) and .2311 (no go).
As you can see, the STI gage is well oversize to fit a standard 1/4-20. If the heli-coil is not a 'locking' type, you can check the heli-coil after insertion using a standard gage, however, in my experience, you want to check the thread prior to inserting the heli-coil with the proper gage.