Make your flies look neat and professional with this Veniard Stainless Steel Hair Stacker.
 
A hair stacker is used to make the hair that you will be tying onto your fly lie straight and uniform.  It also makes it much easier to tie your flies.  Deer hair, for example, once trimmed, is not very uniform, so putting it into a stacking tool allows it to lay more even which means there is less adjusting for you.
 
Hair stackers are an invaluable tool that every fly tyer should have on their bench.