G.T. Here is a method I have used for correcting the hardness of small orifices/screw holes: If the screw hole is hardened excessively, you can temper it by:
Obtaining a slightly undersize steel rod section, mild steel is fine.
Heat rod section to red...it will cool quickly
Add oil, like WD40, to the hole. This oil boils off at about 425f
Insert heated rod section into screw hole ..wait until oil smokes off completely. This should reduce the hardness to the point to can thread it.
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