This Danville thread is tough, well-made, and comes in the standard for many different applicable colors; that lay flat. I like Danville threads for tying smaller trout dries and nymphs to bass jigs for spin casting, and rarely make another brand choice. It's good stuff.
This thread is tougher than tough. When I need a thread that's gonna hold strong and stay secure when hit by those big predatory fish, I always go with this stuff. It ties relatively flat as well which is a bonus.
This flat waxed thread by Danville is a solid thread that is great for tying almost anything. I use it mostly for saltwater flies, but have started using it on some trout patterns as well. It holds up great to a hungry mouth and allows me to get a little more use out of a handmade tie before its tore up. Great all-around thread!
Danville's Flat Waxed Nylon thread ties smaller than its 210 denier would lead one to believe. I just completed dozens of size #10 Golden Retriever flies in peach, white, and root beer with red Flat Waxed Nylon as the underbody and tying thread. This thread replaced the red floss often used for this pattern. By spinning the bobbin holder in one direction or another to twist or untwist this thread one can tie flat, even bodies or corded thread for faster build-up or strength. Moreover, an economy of wraps mitigates unintended build-up, but its flatness produces smooth, glossy heads. I see it is compared to GSP, which is comparing apples to oranges. The colors of Flat Waxed Nylon are quite bright with many, many choices of colors. The brightness of the red underbody of the Golden Retriever easily shows through palmered Estaz, which is why trout are so attracted to this fly. Most Pacific salmon flies are tied with Flat Waxed Nylon. Since Flat Waxed Nylon is multi-stranded, it can be split for dubbing. The colors of GSP are anemic, washed out, and few in number. True, the strength of GSP thread is much greater than Flat Waxed Nylon, which may be needed for spinning deer hair, but how much strength does one need for most flies. The more I apply Flat Waxed Nylon as the tying thread for flies, the more I appreciate its qualities. Great stuff!