UNI pre-waxed thread is a very popular tying thread, available in 200Yard spools in a variety of colours. 6/0 size is the most commonly used size of thread, if you are tying smaller than size 16 hooks you may want to use size 8/0 thread. If you are tying larger flies, for example pike flies it is best to use UNI Big fly thread. Image colour may vary from the actual product colour.
