Brakequip Fitting - Male Swivel Nut M10 X 1

The swivel nut rotates independently during installation, which lets you thread it onto the port without the brake line itself turning along with it. That's the whole point of the swivel design. Once it's torqued down and seated, the connection holds firm. It's especially handy when you're working in a tight spot where you can't easily spin the line to get it started.