Eumer's plastic tubes are made for easy and fun tube fly tying. Plastic tubes are suitable for the inner and outer tube of a tube fly. The Xsmall tube goes inside the M tube. The Small tube goes inside the L tube. The tube fly can be finished with the Eumer conehead. The suitability of the conehead for the plastic pipe is marked on the product. Eumer tube flies are used for all fish in all waters. (Salmon, trout, rainbow trout, perch and pike)