T-tubes are a basically a brass US tube with a flange. The flange is a very simple modification, yet very nice for certain applications. For patterns with a thread head it creates an easy flange to tie against and greatly increases durability. The inside diameter is 2mm to fit our 1.8mm plastic tubes. If you want to finish your pattern with a cone, than our deep recess cones will fit over top of the flange, for a very strong cone connection. Our T-tubes are available in 3 sizes; 15mm, 20mm and 25mm.