This stuff is a headache, hope this helps:
I think what you are holding is an "AN3 female fitting" I could be wrong though. I spent way too much time trying to figure out all this brake fitting stuff, and opted to go the simplest, strongest route I could think of. If you want custom lengths, just use 3/16" IFF/IFM (International flare female/male), and get Cupronickel brake lines. Buy a 3/16 brake line flaring tool
(this one is working great for me). The line is easy to bend by hand, and you can cut the line to size. If you need the line to flex for a suspension compenent or something, then just get a cheap section of rubber brake hose that has the same fitting type. They also make AN3 to IFF/IFM adapters if you want to keep those rubber hoses and create a lenghts. 3/16" Cupronickel with the double flare from the flaring tool is the way to go, just get a little metal tube cutter with cutting wheel to cut the line. Cupronickel is easy to bend by hand, no fancy tool needed. IFF/IFM just refers to the fitting type, aka, IFM has the threads on the outside, IFF has the threads on the inside. FIttings are cheap too. Per another user on here,
I used this stuff on the male threads. I was, and still am, against compression fittings, when possible. Simply due to the easy ability to overtighten and strip stuff. Threaded lines (like what you are holding, and IFF/IFM/AN fittings can be repeatedly taken off/reinstalled. To a certain degree, compression fittings are one-time-use, Here is some good general info on the fitting types. And from my understanding AN3 and 3/16 iff/I'm have the same thread, but different flare angels. Iff/IFM for the win in my opinion. They sometimes are just called a "double-flare." Basically you squish the end of the line twice in a flaring tool with 2 sets in order to make your flare. Don't forget to slide on your fittings before doing this if it's the route you go.
Just to make it more confusing, I swapped my MCP compression fittings om the master/caliper to IFF, and found out the housings from MCP are NPT threads!
https://www.speedwaymotors.com/the-toolbox/automotive-fittings-iff-ifm-an-and-npt/28780