on the intake side of a throttle body?
I got one off of fleabay and there's a hole about 5/16 thread through the body near the end where the boot would go. It has obviously been added later.
Any clues?
Actually most of the Nitrous nozzles I have seen and used are 1/16npt which is very very close to 5/16nf. Its kinda a pain because 1/16npt taps are not something you just run to the hardware store and purchase.