Get the right size & thread tap for the pressure tap your going to install. Drill the hole and slowly screw in the tap a couple of turns then back it out a quarter of a turn then in again a couple turns then back it out a quarter. Repeat this until the tap is fully in to the hole. Not rocket science, pretty easy. The pressure nipple package will have the size and thread dimensions that will work. Usually but not always 6-32. The 6 is the size of the hole. the 32 is the number of threads per inch. If it is a 6-32 tap then the hole size to drill is #36.