This morning I measured out the fet placement on the heat sinks, then wrote the g-code to do it on the cnc. I debugged the g-code on the cnc too. Now I can drill and tap all 18 holes in 3 heat sinks with ease. They will all be tapped for 4-40. 3mm would work too. I suppose I could drill a clearance hole and use nuts on the back side too.