Ultra GSP is the strongest thread on the planet. Boasting steel-like strength for its weight, this thread really lets you put the pressure on! Our gel spun polyethylete is supple, ties flat and is available in the largest selection of sizes and colours. GSP 100 has all around versatility for fresh and saltwater flies. It is an excellent thread for bonefish and permit fly patterns and our favourite pick for trout and smallmouth bass streamers. 50 yard spools. The colours in this 4 spools combo pack are Black, White, Yellow and Brown.