Strong, smooth, flat, lightly waxed, slow building fly tying nylon thread. UTC 70 has a breaking strength of about 1 lb. and is recommended for size 14 and smaller flies. Same size as Danville 6/0. 100 yd. spools. UTC 140 has a breaking strength of about 2 lb. and is recommended for sizes 6 to 14 flies. Same size as Danville 3/0. 100 yd. spools.