Nut/ferrule, no twist, 1/16" fingertight, PEEK ferrule

No twist fittings offer the convenience of a one-piece fitting while solving a problem inherent to such designs. In other one-piece designs, the ferrule rotates against the fitting detail, creating particulates. The no twist design has a separate ferrule that snaps into the nut, so it's attached but still free to avoid rotation during tightening. Since the ferrule is not machined onto the nut, it can be made from a different material.