Our metric, flangeless outer nut is easy to use, eliminates the need for flaring and is reusable. It is made of It is made with versatile Delrin (acetal resin), which allows the nut to resist cross threading or loosening during use. It comes with an M6 flat bottom connection configuration and is for 1.8mm, 2.0mm, 3.0mm and 1/8" OD tubing.