SemperFli Nano Silk thread is regarded as the tying thread choice of professional fly tyers worldwide. Specially formulated Gel Spun Polyethylene (GSP) Nano Silk fly tying thread is super strong with endless possibilities for micro to medium flies. Virtually unbreakable and still capable of being split down for dubbing twists, Nano Silk lets you confidently tie the smallest flies without your thread breaking! Using Nano Silk eliminates thread build-up and is ideal for fly tying when you want to hide the thread.Specifications and Features: 10 times stronger than steel of the same diameterLays perfectly flat with no build-upSemperFli Nano Silk 30 denier 18/0Breaking strain 2.51lbRecommended hook size 16 to 32