– The US-Tube has been on the market for many years, very popular in Scandinavia. You can use it as a body, our as a weight under the dubbing, flatbraid ect. The FF Classic US-Tube fits perfectly on the FF Plastic Tube 1.8mm. We have it in 4 sizes: 6mm 0,20gram – 10mm 0,30gram – 13mm 0,40gram – 16mm 0,50gram.