#1469, "RE: what are the tap specs for the GM sensors" In response to In response to 2
A 9/16" drill is often used and will work with a 3/8" NPT tap, but it'll be a little tight when you start the tap. The correct drill size for a 3/8" NPT tap is 37/64".
For anyone looking to buy a 3/8" NPT tap, you will not find it at any auto parts store. You also will not find it at Lowes, Home Depot, etc. You can get cheap carbon steel pipe taps at places like toolbarn.com though.