Quick question about Noveske BCG's

Purchased a BCG directly from Noveske, I noticed these things are no longer “N” marked, this one was “F” marked.

What does the “F” mean?

Mine us “F” marked as well. I would also like to know the difference.

I would start by asking Noveske. I also wouldn’t be concerened if it was marked X, Y or Z as long as it is correct.