I thought it was 3/8 npt but it doesn't go in far enough.
i only turn 3-4 turns and out rail was already cracking so I backed off and some thread dmaged already.
and thread is so close to injector feed hole.

I think I might screwed rail but I still got some thread left somay be I just cut the end..

anyway what thread should be I mean other side 3/8 was OK but this firewall side
seems a little bit smaller..