my S475 is 1/4" npt , then the fitting i bought converted it to -6 AN for the oil feed line . in short a "T" ( twins ) 1/4" NPT for turbo then other 2 -6 AN for the feed lines .
We run -4AN on the S400's and that is fine. If you look at the actual passages that are drilled below the 1/4" NPT -4AN will feed it fine. -6AN is fine as well, just a little harder to route.
I have physically screwed in my 1/4" NPT fitting so yes they are 1/4" . and Brayden is right -4 an is plenty , i chose 6 but still may go -4 , i thought -6 might be some extra insurance for feeding the 2 turbo's
Now you want a Male?