Our Super Flangeless Ferrule w/Stainless Steel Ring 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. Our ferrule assembly has a 1/4-28 Flat-Bottom port configuration and is for 1/16OD tubing. It also comes in yellow as a single and in a 10 pack.