IDEX PEEK Super Flangeless Ferrule is designed specifically to eliminate loosening of fittings due to tube twisting, hold tight even during vibration and delivers the highest pressure holding for flat bottom fittings that we offer. IDEX ferrule assembly has a 1/4-28 thread port configuration and is for 2.5 mm OD tubing. It comes in natural as a single and in a 10 pack.