Im installing a Ligtning IAT sensor on the car as the boost is popping the old one out. I need to know what thread the sensor is so I can drill and tap the boost pipe for it..
If you already have the Lightning IAT and a tap and die set, all you have to do is try various dies over the IAT until you find the correct die. Then you know which tap to use.
Well, I'm pretty sure it's a "straight fit" or 3/8-18 NPSF (this is what the print calls for). For pressurized applications, they guideline is to use a tapered fitting in a straight fit hole.
However, the NPT will probably hold up. If you have the NPSF, use it. If not...