Richard, I am learning a lot here. Which is great but, I do not want it to be at the expense of one of my precious castings.…! Yes, I chased the single point threading with a 1/32 tap. I’ve discovered that even though the tap feels like it’s going in square and straight When rotated and supported by hand; it’s probably not. I finally had the sense to mount the tap at one end with a live center, and then it negotiated straight as an arrow. I’ve also learned how aggressive a new large quality tap can be where did all these giant chips come from? I thought I just single point threaded it! Yes, the spring phenomenon with my cutter was actually visible and as the other person mentioned, I think maybe the back or bottom of the cutter is rubbing against the side of the work. Something continuously is making my leave crash. It’s rubbing it putting the brakes on… I’ve spent way too much time trying to do the single point threading on only one cylinder boss . I probably need to reposition the cutter go to the 55° and use a compound angle for the internal threading… When you look on a tap chart for the drill to be used for tapping 1–32 it says to use a 15/16 drill , is that size the same as the minor diameter? I don’t think it is. And yes, I do have the engineers handbook… also, I believe my depth of cut will be the difference between my major diameter and minor diameters. Also, I am still confused of where these threads are to be placed within the casting (crankcase casting bosses ) Chenery shows that the threads are 0.187 inches deep… Not sure if that means starting at the top going in or after going in 0.187 inches? Also, I believe I do understand the holes configuration, which serves as an intake valve for each cylinder…