Does anyone know the thread size for the oil pressure port on a smallblock chevy?

Thanks in advance,

1/8" pipe

I'm talking about the port at the back of the block right next to the distributor. It is much bigger than 1/8". I have an Auto-Meter mechanical oil pressure guage, and according to the instructions, it is a 1/4" adapter, however I need to clean up the threads on the hole, and a 1/4" NF thread chaser does not look at all correct. Is there another port I can use, or am I really confused?

1/4" pipe threads are almost 1/2" in diameter. Pipe is measured on the ID. The oil pressure port is 1/8" pipe which is about 1/4" on the OD.

That makes sense. I still am not sure what size thread chaser I would need to clean out the threads on the pressure port itself. Can you help with this?

Thanks.

1/8 in. NPT tap is what you need.

Thanks to all who responded, i went out on the web and got myself educated on the pipe sizes.