Walk into any fly shop or browse online, and you'll be met with a bewildering array of fly tying threads. Different materials, countless colors, and varying sizes often labelled with numbers like "6/0," "8/0," or a figure followed by "D" like "72D." Understanding these sizes is crucial for tying durable, proportionate, and effective flies. One of the most common and standardized measurements you'll encounter is denier. But what exactly is it, and why should you care?
This guide will demystify denier, explain how it impacts your tying, look at common denier values like 72D, 136D, and 400D, and clarify how the older "aught" system relates to it, specifically for popular brands like UNI-Thread.
What is Denier? The Technical Definition Made Simple
Denier (often abbreviated as 'D') is a unit of measurement used to determine the linear mass density of a fiber. Simply put, it's the weight in grams of 9,000 meters of that specific thread.
- Lower Denier = Thinner/Finer Thread
- Higher Denier = Thicker/Heavier Thread
For example, 9,000 meters of a 72 denier (72D) thread weighs 72 grams, while 9,000 meters of a 400 denier (400D) thread weighs 400 grams. This system provides a reasonably consistent way to compare thread thickness, especially within the same material type (like polyester or nylon).
Why Denier Matters in Fly Tying
Understanding denier helps you choose the right thread for the job, influencing several key aspects of your fly:
- Bulk Control: This is perhaps the most significant factor. Using a thread that's too thick (high denier) on a small fly will quickly build unwanted bulk, making it difficult to achieve a neat head or tie in materials cleanly. Conversely, a very thin thread (low denier) on a large pattern might require excessive wraps to cover the hook or secure bulky materials.
- Strength: Generally, higher denier threads of the same material are stronger. However, material type plays a massive role. Gel Spun Polyethylene (GSP) threads, for instance, can have incredibly high breaking strength even at relatively low deniers compared to standard nylon or polyester.
- Application:
- Low Denier (e.g., 72D): Excellent for small flies (size #18 and smaller), midges, delicate dry flies, and situations where minimal thread build-up is essential. Ideal for creating tiny, neat heads.
- Medium Denier (e.g., 136D): A versatile workhorse range suitable for a wide variety of patterns like nymphs, standard dry flies, and smaller streamers (sizes approx. #8-#16). Offers a good balance of strength and low bulk.
- High Denier (e.g., 400D): Perfect for large flies, saltwater patterns, bass bugs, spinning deer hair, and applications demanding maximum thread strength and pressure. This thread builds bulk quickly, which can be advantageous for creating tapers or securing heavy materials.
Exploring Common Denier Values:
- 72 Denier (72D): This is a fine thread, often equating to an 8/0 size in brands like UNI. It's prized for tying small trout flies, midges, and delicate dries where minimizing bulk is critical. It allows for many wraps without overwhelming small hooks. Check out options like UNI-Thread 8/0 Black (72 Denier) or UNI-Thread 8/0 Olive (72 Denier). Other popular colors include White, Red, Yellow, and Olive Dun.
- 136 Denier (136D): This medium-sized thread is a very popular choice, corresponding to UNI-Thread's 6/0 designation. It hits a sweet spot for general trout patterns, nymphs, and smaller streamers. It's strong enough for most freshwater applications without being excessively bulky. We carry a wide range, including UNI-Thread 6/0 Black (136 Denier), UNI-Thread 6/0 Olive (136 Denier), and other essential colors like White, Red, Yellow, Gray, and Olive Dun.
- 400 Denier (400D): This is a heavy-duty thread designed for big tasks. UNI markets this as their "Big Fly" thread. It's ideal when you need serious strength for large saltwater flies, bulky bass bugs, spinning coarse deer hair, or attaching heavy materials like lead eyes without constant breaking. Explore options like UNI Big Fly Thread Black (400 Denier), UNI Big Fly Thread Olive (400 Denier), or other colors including Red, White, and Yellow.
What About the "Aught" System (3/0, 6/0, 8/0)?
The older "aught" system (e.g., 3/0, 6/0, 8/0) predates the widespread adoption of denier. Its main drawback is inconsistency between brands – a 6/0 from one manufacturer might have a different denier (and thus thickness/strength) than a 6/0 from another.
However, within a specific brand like UNI-Thread, the aught sizes generally correspond to consistent denier values:
- What denier is 8/0 thread? For UNI-Thread, 8/0 is 72 Denier (72D).
- What denier is 6/0 thread? For UNI-Thread, 6/0 is 136 Denier (136D).
- What denier is 3/0 thread? For UNI-Thread, 3/0 is typically around 220 Denier (220D). (Note: UNI Big Fly at 400D is even heavier duty).
It's crucial to remember this mapping is brand-specific. Always check the denier rating if comparing threads across different manufacturers.
Fly Tying Thread Denier Chart (Approximate Guide)
| Denier Range (Approx.) | Common UNI Aught Equivalent | Typical Material | Common Uses |
|---|---|---|---|
| 50D - 75D | 8/0 | Polyester, Nylon, GSP | Tiny Midges (#20+), Small Dry Flies, Delicate patterns, minimal bulk needs |
| 100D - 150D | 6/0 | Polyester, Nylon | General Trout Flies (#8-#16), Nymphs, Medium Dries, Smaller Streamers |
| 200D - 250D | 3/0 | Polyester, Nylon, GSP | Larger Nymphs/Streamers, Bass Flies, Smaller Deer Hair work, Saltwater (#2-#8) |
| 250D - 400D+ | Big Fly / 1/0 | Polyester, Nylon, GSP | Large Streamers, Pike/Musky Flies, Heavy Deer Hair, Saltwater Flies (#1/0+) |
Note: GSP threads offer higher strength at lower deniers compared to Polyester/Nylon.
Choosing the Right Denier for Your Flies
Selecting the best thread denier involves considering:
- Hook Size: Smaller hooks generally require lower denier threads.
- Fly Pattern: Delicate dries need fine thread; bulky streamers need stronger, often thicker thread.
- Materials: Are you tying in fine hackle or spinning coarse deer hair? Stronger thread is needed for applying pressure to bulky/tough materials.
- Personal Preference: Some tiers prefer the security of slightly heavier thread, while others prioritize minimal bulk above all else.
Don't be afraid to experiment! Having a few different deniers on your bench (like a 72D, a 136D, and perhaps a 200D+ or GSP) covers most fly tying situations.
Conclusion
Understanding thread denier moves you beyond simply grabbing a spool labelled "6/0." It empowers you to make informed choices about thread thickness and suitability for the specific fly you're tying. Knowing that a lower denier means a finer thread for less bulk, and a higher denier means a thicker, often stronger thread for bigger tasks, is key. By matching the denier to your fly tying hooks size, pattern style, and materials, you'll tie neater, more durable, and ultimately more effective flies.
Ready to stock up? Explore our wide selection of fly tying threads to find the perfect denier and color for your next pattern.
Faq
1. Q: What does denier mean for fly tying thread?
A: Denier (D) measures the linear mass density (thickness/weight) of fly tying thread. It represents the weight in grams of 9,000 meters of that specific thread fiber. Simply put: lower denier numbers indicate thinner, finer threads, while higher denier numbers indicate thicker, heavier threads.
2. Q: Why is denier important when choosing fly tying thread?
A: Denier is crucial because it directly impacts fly bulk, thread strength, and suitability for different fly sizes/types. Finer denier threads (e.g., 72D) are best for small flies to minimize bulk, while heavier denier threads (e.g., 400D) provide strength needed for large flies, spinning deer hair, or applying high pressure.
3. Q: What denier is 8/0 fly tying thread?
A: The denier for 8/0 thread varies slightly by brand. However, for the popular UNI-Thread brand, 8/0 thread corresponds to 72 Denier (72D). This is considered a fine thread, ideal for small flies (#18 and smaller) and midges.
4. Q: What denier is 6/0 fly tying thread?
A: Similar to 8/0, the exact denier for 6/0 can differ between manufacturers. For UNI-Thread, their 6/0 thread is 136 Denier (136D). This is a versatile, medium-sized thread suitable for a wide range of general trout patterns, nymphs, and smaller streamers (approx. #8-#16).
5. Q: What denier thread is best for large flies or saltwater patterns?
A: For large flies, saltwater patterns, bass bugs, or spinning tough materials like deer hair, a higher denier thread is recommended, typically 200D or more. Threads like UNI Big Fly (400D) or strong GSP (Gel Spun Polyethylene) threads offer the necessary strength and bulk to secure heavy materials and withstand strong fish.