Manifold stud nut size?

I have new manifold to midpipe studs from Ford part N808447-S100 btw. They did not have the nuts. Found nuts at Home Depot. The thread on the stud is tapered so it locks on, thus I can only thread the nut about 3/8 inch or so before it locks on. Not sure whether the nut is m12-1.75 or m12-1.50 or another? Which am I supposed to use? Don't want to put one on to find out it is the wrong one, strip threads, etc.

Thanks

i know when they came off....err snapped off, the socket was a 15mm, i think... the 1/2 inch nut i tried seemed too loose although with the taper on the stud it does tighten but the 12mm .175 fits more like the original. i am thinking if it is too tight i may blow it up. tough to tell cause of the taper.

went to Ford dealer. he pulled up specs of nut. confirmed it is m12 - 1.75