The inside looks just like a 1/4 or 3/16 female brake line type flare.
I ended up putting the 1/8 nut on the copper line then I installed a compression fitting on the line. Next I cut the 1/8 compression fitting off the line leaving only the 1/8 flare type fitting with the compression ring. I then took the dremel and trimmed up the ferrule and tbg.
It works great and I have about 35-40 psig
