Thanks for the input and correction

I've found a pdf indicateing that theres such a thing as an M8x1.25 (male) to 1/8 NPT (female) adapter but thus far I can't source one. I've called local and google search results fittings suppliers with no luck thus far. There is an oil pressure gauge kit that includes this fitting but do I want to spend $30 or more for it?
A machining question.
A 1/8 NPT tap requires an 11/32 drill bit which I have. I'm leaning to trying to drill out that female M8 nut thats spot welded in the tank and retap it to 1/8 NPT.
Is there enough metal in the nut to go oversize. Will the nut hold and not break loose in the tank?
Just weighing all the options.
Dave