Simply tie in one of these tails at your desired length off the back of the shank and let the action of the current do the rest of the work. The elasticity and stretchiness enable this product to move like crazy in the water. You can mark this tail as well--simply stretch the tail until its tight and use a permanent marker. Available in various colors and 3 different sizes: small (6-12), medium (1-4), and large (1/0 & up). 7 tails per pack. The spikes add opportunity for additional movement and also provide finer detail to the tail end of the fly.