Danville Spiderweb thread is100yds of 16/0 or 30 Denier thread. Spiderweb fly tying thread is about as small as fly tying thread gets and is usually used for tiny flies like Trico mayflies, micro midge patterns, and other size 20 to 28 flies where minuscule is the rule. Is it strong, you ask? No. But it is small and is perfect for those little munchkin flies that trout sometimes demand.