Thanks for the help These heads are new angle plug alum. castings going on a 355 12.5 roller cam moter. My ? is when i install a plug i can still see threads exposed inside the chamber. this seams to me to be a place for detanation to start. would it be best to blend these threads into the chamber to eliminate a hot spot in case i put the nova on the bottle, Also the heads use 5/8gasket seat 3/4 reach spark plug. Could anyone suggest a plug mfg. that has this style plug in many different heat ranges thanks