UTC Ultra Thread is designed to be a fly tying string and not just an ordinary thread off the shelf. UTC Ultra Thread is a flat fly tying string made of nylon material, the fact that it is flat allows you to build very nice bodies without too much "build-up".
The thread comes in sizes 70 and 140 denier, where 70 is the thinnest and 140 the coarsest. Fly Fishing Market offers all the fly tying line from UTC.
