Hi guy I was on ebay recently looking for a header and noticed that some of them have a hole in one of the top pipes, is this hole for a sensor ?. some of the headers up for auction seem not to have any. thanks for the help

 

Maybe for the o2 sensor.

 

yup, and if it doesnt have a hole you're gonna have to have a bung welded in for the o2 sensor.

and some tp for your bunghole.