Available in both flanged and unflanged, the flanged tube has a lip around the head and will stop your thread slipping off the end of your tube and stop it unravelling. The flanged option is designed for flies that are not being finished with a conehead.
The unflanged version is for flies that are going to be finished using a conehead. The unflanged head is smooth with no lip which allows the cone to slip over easily and give your fly a nice, neat finish.
These high water tubes are also the same weight as Tungsten, adding extra weight to your fly to help them get down faster.