Veevus GSP (Gel Spun Poly) Fly Tying Thread- 30 Denier is the worlds thinnest GSP thread which is equivalent to 18/0. GSP (Gel Spun Polyethylene) Thread is by far the strongest thread on the planet. The Veevus G.S.P. thread has been designed with a slight twist preventing it from opening up, and thereby making tying with it a breeze. It lays completely flat and is the smoothest thread to spin hair with. 30 Denier is only available in white. Get 100, 150 and 200 denier here, Veevus GSP (Gel Spun Poly) Fly Tying Thread. 75 meters per spool (which is 67% more thread than offered by anyone else in the industry).