This steel brake adapter has a male 3/8-24 inverted flare (concave) fitting on the short end and a 3AN male (3/8-24, 37° convex) on the long end. The 9/16" hex is large enough to support a crush washer (sold separately) when sealing the 3/8-24 inverted flare side against a flat faced port. Sold individually.
We also offer a standard Short 3AN Male to 3/8-24 Inverted Flare Adapter (Part No. 3265-2) for installations that do not require the extended neck on the 3AN end.