6/0 & 8/0 UNI-Thread is a general fly-tying thread of continuous polyester filaments. The wide range of colors meets virtually all fly-tying needs. UNI's exclusive waxing process produces a thin coating to reduce that annoying build-up of wax in your bobbin tube. 6/0 is for hook sizes 10 to 16 and 8/0 is for hook sizes 14 to 24. 200 yard spools.