I need to go from 1/8" NPT Male to 1/4" NPT female. I'll be using for a gauge to check the fill pressure between my compressor and gun. Can I use a brass fitting or does it need to be a special HPA fittings.
the fittings you buy MUST be rated for the pressure you are putting in it ,,this one is NOT rated
https://www.amazon.com/Brennan-5405-02-04-SS-Stainless-Fitting-Reducing/dp/B004Y18CXI/ref=sr_1_9?keywords=1%2F8+npt+female+to+1%2F4+male&qid=1578533054&s=industrial&sr=1-9
do not use it
try this
https://www.fastenal.com/products/details/421420 5000 psi