Precision fly tying starts with using the right thread. 6/0 UNI-Thread is made of continuous polyester filaments, slightly bonded for uniform lay. The filaments are not twisted, so the thread is easy to tie and will lay virtually flat on the hook. Result: easy handling with crisp, clean wraps. 136 denier. Made of continuous polyester filaments Slightly bonded, no twist Ties easily and lays virtually flat on the hook 136 denier.