Broke my first 4-40 tap in the 9cyl front cover. Was able to clear and re-tap. I thread milled 95% of the 4-40s on this project (several 100's of holes) and never broke anything in the hole. I tap 12 4-40 threads and break a tap... I did not know how to thread mill before when I made this part at the beginning of the project. I very much dislike hand taps.... Rant over.