Existing threads are often too bulky for tiers who work with hooks smaller than size 20. This extra-fine (20 denier), white, polyester thread, is amazingly strong for its diameter. Perfect for caenis, trico, tiny baetis, midges, micro-caddis, and realistic patterns. Hit with a permanent, waterproof marker to get the desired color. Breaking strength is 4 ounces. UNI Trico 17/0 is available in 200 yard spools.