I would like you to look at a production part my new day job produces out of 4140/4150 up to 48 HRc. It has an internal 90 degree thread utilizing carmex style laydown threading inserts. I understand Swift Tool (in the Seattle area) sends these to Michigan for modification from a standard 60 degree insert, an some coating is also applied. I wonder if it is you that the send the work to. If you are interested let me know.
I hope you are enjoying the three flute mics I sold you.
I am happy to give "likes" when I feel they are deserved. PM is much stronger with the specialists such as yourself that can help with knowledge of carbide inserts and their grinding expertise. I thank you for your contribution. I know what its like to feel overwhelmed by the vast knowledge this site amasses. Humble gents like yourself have made me feel more comfortable sharing when I find a thread I can contribute to.