Hex head fitting for UHPLC connections up to 20,000 psi. Must be used with EXP titanium/PEEK hybrid ferrules. The ferrule is not permanently swaged to the tubing so it is reusable multiple times. Requires a 1/4" wrench, and for best results, tighten a maximum of 1/4 to 1/2 turn past hand tight for a 20,000 psi seal. For 1/16" OD stainless steel tubing. Replacement ferrules are REST-25935 (ea) or REST-25936 (10/pk). Not recommended for use with PEEK tubing. Replacement for 220-91522-38.