These nuts are for use with VICI Jour double ferrules, which grip the tubing twice for added stability. They fit any 10-32 fitting, The fingertight version may be hand-tightened for operation at up to 420 bar (6,000 psi). The hex-head version can be used for connections that are difficult to reach or closely spaced. They fit any 10-32 fitting and work in virtually any female 1/16" fitting.
For more information on PEEK, refer to Properties of Polymers and Chemical Resistance of Materials