Hello, I'm not usually in this chat but I had come across something that I cant figure out. If this is not the right place please direct me to the right place.

I drilled a hole with a 9/16 drill bit so a 9/16 hole. What tap size do I need to thread the hole? It is an npt thread like for aircompressor.

@ScientistSmithYT Usually one knows the needed thread before, and then uses a thread chart to find out about the needed hole size

What is the needed thread size?

@Martin They don't give a thread size for npt fittings. So I don't know

@Martin I did a quick search and it gave me a chart for npt pipe threads. It says 3/8 inch pipe is 18 TPI

I do know that the hole I drilled at 9/16 is slightly smaller than the threads but the solid part of the pipe is a tiny tiny bit smaller than the hole

This is the thread and hole I have.