Untangling Fly Tying Threads: A Quick Guide

Fly tying thread seems simple, but choosing the right one can significantly impact your fly's durability, profile, and how easily it comes together. I noticed a significant improvement in my fly tying once I had better understanding of the different types of threads and the tying situations each more suited to. Let's delve into the basics and improve your tying.

What's it made of? The Material Matters

Fly tying threads generally fall into three main material categories:

1. Nylon: The traditional choice. Nylon threads often have a bit of stretch, which can be forgiving but also requires consistent tension control. They tend to absorb water and are often available waxed, helping to grip materials. Good for general purpose tying, building body tapers, and flies where a little bulk isn't critical.
2. Polyester: Generally stronger than nylon for its diameter and has less stretch. It's more resistant to water absorption and UV damage. Polyester is great for smaller flies where minimizing bulk is important and for situations needing more strength without added thickness. Many tyers prefer it for dry flies.
   
3. GSP (Gel Spun Polyethylene): The powerhouse. GSP is incredibly strong for its diameter, has virtually zero stretch, and is very slick. This makes it ideal for spinning deer hair, securing bulky materials on large streamers or saltwater patterns, and creating durable heads on small flies with minimal wraps. Caution: Its strength and lack of stretch mean you can easily cut through softer materials or break hooks if you apply too much tension. It's also slippery, requiring secure knots

Understanding Thread Sizes: Denier vs. Aught (/)

This is where confusion often creeps in:

• Denier: This is a direct measurement – the weight in grams of 9,000 meters of the thread. Higher Denier = Thicker/Stronger Thread. (e.g. 70D, 100D, 140D, 210D). This is the most consistent way to compare threads across brands.
  
• Aught System (/0): This is an older system where, generally, more zeros = thinner thread (e.g. 8/0 is thinner than 6/0, which is thinner than 3/0). However, this system isn't standardized across brands. A 6/0 from one company might be closer to an 8/0 from another in actual thickness so use it as a rough guide within a specific brand. For example, 6/0 Danville´s Flymaster is 70 denier, whereas 6/0 Uni-Thread is 135 denier.

Major Brands You'll Encounter

If you go into your local fly fishing store, you'll frequently see threads from these manufacturers:

• Semperfli: Known for their extensive range, including the popular Nano Silk (GSP available down to incredibly fine 24/0 or 18D!), Classic Waxed (Polyester), and Spyder (fine Polyester).
• UTC (Ultra Thread): Famous for their flat-lying nylon (UTC 70, 140) and polyester (UTC 140 Ultra Wire Substitute) threads. They cover hooks well with minimal bulk.
• Veevus: Offers a wide range of GSP and Polyester threads known for their strength and consistent quality across various deniers (e.g., Veevus 10/0, 16/0 GSP).
• UNI-Thread: A long-standing classic, offering reliable waxed nylon (like the popular UNI 8/0) and polyester options in a vast array of colours.
• Danville's: Another staple, known for their Flymaster 6/0 (a flat, waxed nylon) which is affordable and very reliable.

Choosing the Right Thread: When to Use What

• Small Flies (Size 18+): Go thin! Think 8/0, 10/0, 12/0 or finer (~30D - 70D). Polyester or fine GSP helps keep bulk down. Semperfli Nano Silk, Veevus 16/0, UNI 8/0 (used sparingly).
• General Trout Flies (Size 12-18): Mid-range threads work well. 6/0, 8/0 or ~70D - 100D. UTC 70, UNI 6/0 or 8/0, Veevus 10/0 or 12/0, Semperfli Classic Waxed 12/0.
• Large Flies (Streamers, Saltwater, Bass flies, Size <12): You need strength and maybe some bulk. 3/0, 1/0 or ~140D - 210D+. UTC 140, UNI 3/0, Veevus GSP (100D+), Semperfli Nano Silk (100D+).
• Spinning Deer Hair: GSP is the top choice due to its strength and ability to flare hair without breaking. Choose a suitable denier (100D+ is common).
• Dubbing Loops: A stronger thread (Polyester or GSP) is often preferred to handle the twisting and tension.
• Building Body Bulk: Waxed nylon threads excel here.

My Top Fly Tying Thread Tips

1. Match Thread to Hook: Use the finest thread appropriate for the hook size and materials you're using to minimize bulk and create neater flies.
2. Master Tension Control: Apply firm, consistent pressure. Too little leads to loose wraps; too much can break thread or cut materials (especially with GSP). Practice helps you find the sweet spot.
3. Wax On: Even if a thread is pre-waxed, adding a touch more wax can help control unruly materials, make dubbing easier, and add a bit of waterproofing/durability.
4. Spin to Flatten/Cord: Many modern threads (UTC, Veevus, Semperfli Nano) lie flat. You can untwist them (usually spinning the bobbin counter-clockwise) to get a flatter profile for less build-up. Spinning clockwise cords them up for splitting (for split-thread dubbing) or extra grip.
5. Use a Quality Bobbin: A good bobbin protects your thread spool, provides smooth tension, and prevents fraying. Ceramic-tipped bobbins are excellent, especially for GSP, as they reduce friction and wear.

Final words...

Choosing the right thread becomes easier with experience. Don't be afraid to experiment with different materials, sizes, and brands to find what works best for your tying style and the flies you create. Understanding the basics is the first step to building better, more durable flies. Happy Tying!

Videos links

Explaining Fly Tying Thread - Ryan Ratliff from Mad River Outfitters explains fly tying thread: denier, aught, materials, and brands

Understanding Fly Tying Thread with Charlie Craven