Fly Tying Thread Sizes | Choosing the Right Thread

The foundation of every successful pattern is the fly-tying thread used to secure materials to the hook. Knowing how to manage scales and measurements is a main skill for anyone who is serious about fly tying. Yes, it might seem like a small detail, but the strength and diameter of your tying thread will dictate how your final fly performs in the water. Let's talk more about fly fishing thread size.

Denier & Aught Systems

When exploring fly-tying thread sizes, you'll come across two main measurement systems.
The traditional aught system, such as 6/0 or 8/0, has been around for some decades. In this system, a higher number indicates a finer thread, while a lower number signifies a thicker thread.
But keep in mind that this system lacks consistency between different brands. This led to the rise of the denier thread system, which is based on a standard weight measurement. Denier represents the weight in grams of 9,000 meters of thread. This provides a more scientific way for fly tyers to compare the actual thickness and mass of the products they use at the bench.
Picking between thicker threads and thinner threads depends on the specific task at hand. For example, a 70 denier thread is a common choice for mid-sized patterns. It is strong enough to hold most materials but thin enough to avoid building up excessive bulk.
And if you are tying flies on very small hooks, you might move toward even lighter threads to maintain the profile of the lure.
On the flip side, larger flies and heavy streamers require a more robust thread diameter to handle the tension needed to secure bulky fly-tying materials.

Choosing the Right Thread for the Pattern

Selecting the right thread means balancing durability with the fly’s final shape.
Crafting delicate dry flies? A heavy thread will quickly ruin the proportions and weight of the fly. Using a fine thread allows you to make multiple wraps without creating a large head. This is essential for maintaining the buoyancy of the fly when fly fishing in slow-moving water, where trout fish have plenty of time to inspect your work.
Many people also go for the UTC ultra thread for these applications. The reason is that it lies flat on the hook, which keeps the body slim.
If you are working on bass bugs or large articulated streamers, the requirements change.

These fishing patterns generally involve spinning deer hair or securing large feathers, which require a bit of added pressure.
GSP threads or thicker threads are the best choice for these applications.
They can handle heavy tension without snapping, making them perfect for flaring deer hair.
Thread breakage during a complex tie can be frustrating and may waste a hook.
A key rule is to match the size of the thread to the size of the fly for a smoother tying process.

Exploring Thread Materials & GSP

It is particularly useful when spinning deer hair for large surface lures, as it cuts through the hair fibers to create a dense body that will not rotate on the hook shank.
Another specialized technique to go for is split thread dubbing, which requires a thread that can be easily untwisted and separated into two strands. This allows the tier to insert dubbing or feathers between the strands and then spin them tight. This creates a brush-like effect that gives a decent movement to the fly.
Not every fly-tying thread is suitable for this, so selecting one with a flat profile is a good move. Experimenting with different fly-tying thread sizes and types will help you understand which one works best for your style of tying flies.

Practical Tips for Fly Tyers

A common mistake among new fly tyers is using a thread that is too thick for the hook. While it might seem like a thicker thread is safer, the resulting bulk can make it hard to attach wings later in the process.
Learning to work with thinner threads requires a light bit of touch, but it leads to much more professional-looking results. Also, keeping a variety of fly-tying thread sizes in your kit will allow you to adapt to any project that comes your way.
Working on a tiny midge or a massive predator pattern? Having the right thread on the bobbin is the first step toward success.

Mastering Fly Tying Thread Sizes: Denier vs. Aught

Understanding the relationship between the denier thread and the aught system will make your shopping experience easier. When you see a spool labeled as 70 denier thread, you can generally equate that to an 8/0 or 6/0, depending on the manufacturer.
By focusing on the physical properties of the fly-tying thread, you can make better decisions at the tying bench. When you are out fly fishing, this attention to detail eventually translates into better performance, as your flies are better proportioned to mimic the natural insects in the river.

Plan Your Tennessee Fly Fishing Adventure

To some of the most productive trout and bass fisheries in the southeast, the waters of Tennessee are home. Prefer the technical challenges of the Norris - Clinch River or the rugged beauty of the Little River and Pigeon River? There is a destination waiting for you.
For various fly patterns, the Douglas - French Broad River and Cherokee - Holston River offer diverse opportunities, while the Caney Fork River remains a favorite for consistent action.
Taking your hand-tied flies to these rivers is the ultimate way to test your skills and see how your fly tying holds up against wild fish.
To explore these iconic rivers with expert guidance, book your trip with Frontier Anglers TN.

FAQs

Q1. What is the best thread for small trout flies?

A: For small hooks, an 8/0 fine thread or a 70 denier thread is usually the best choice. The reason is that this helps keep the fly light and maintains the correct proportions for small fly patterns.

Q2. When should I use the GSP thread?

A: GSP threads are best when you need maximum strength without adding bulk, such as when spinning deer hair or tying large bass bugs.

Q3. How do I know if I am using too much thread?

A: If the head of your fly looks bloated or if you find it hard to tie in the final materials, you are likely using a thread size that is too large for the hook.

Q4. Does thread color matter for the fish?

A: While the body material generally covers the thread, the color of the head can sometimes act as the main trigger point. We can guide you and suggest matching the thread to the natural colors found in the beautiful rivers of Tennessee.

Q5. What is the advantage of UTC Ultra Thread?

A: The main advantage is that it is a flat thread. This means it spreads out on the hook, helping fly fishing enthusiasts avoid building up a thick diameter and keeping the fly body natural and slim.

Selecting the Perfect Fly Tying Thread Sizes for Dry Flies and Streamers