Fly Tying Threads

What are fly tying threads?

Fly tying threads are – alongside fly tying hooks – a fundamental material required to create an artificial fly. They are used to secure all materials to the hook shank and to build and reinforce the overall structure of the pattern.

A properly selected thread should offer adequate breaking strength, suitable thickness, profile and color. This is especially important for delicate dry flies as well as for larger patterns that require firm material control.

Thread color also plays an important role, particularly in small dry flies, wet flies and nymphs. A dark thread, such as black, can noticeably darken the fly once it becomes wet. For that reason, the thread color should be carefully matched to the materials used in order to achieve the intended final appearance.

Fluorescent threads are also worth considering. Even a small fluorescent accent on the body, behind the nymph bead, or as a finishing wrap near the hook eye can significantly increase underwater visibility. Such subtle details often improve the effectiveness of nymphs and other subsurface patterns in both rivers and still waters.

Thread sizes and labeling systems

Fly tying thread sizes are commonly described using two systems: the “/0” system and Denier (D).

In the 3/0–16/0 system, the smaller the number before the slash, the thicker the thread. For example:

• 3/0 – thick thread,
• 6/0 – medium thread,
• 8/0 – finer thread,
• 12/0–16/0 – very fine threads for small flies.

The second system is Denier (D). In this case, the higher the number, the thicker and stronger the thread. Our range includes threads from approximately 20D up to 300D, suitable for both small precision patterns and large pike or saltwater flies.

Thread profile and types – flat, round and GSP

Threads also differ in profile. Flat threads allow precise shaping of the fly body and head, and they can be split with a needle to insert additional material before being twisted again. Threads with a more round profile compress materials in a narrower area and are often waxed, which improves grip and control during tying.

A separate category includes GSP (Gel Spun Polyethylene) threads, known for extremely high strength relative to their diameter. They are commonly used for deer hair heads, large streamers and patterns requiring strong thread tension, as well as for very small dry flies and nymphs. Depending on thickness, GSP threads can be used for nearly all types of flies.

How to choose the right fly tying thread?

Thread selection depends on the type of fly, hook size and materials used.

• Dry flies and small nymphs – fine threads such as 8/0 or approximately 20–70D.
• Medium nymphs and wet flies – 6/0 or approximately 70–140D.
• Trout streamers – stronger standard threads 140D or 6/0, and GSP up to 70D and above (GSP 70D works exceptionally well for deer hair heads in patterns such as muddlers).
• Large pike flies and deer hair patterns – GSP 100D–300D with high breaking strength.

Proper thread thickness helps maintain correct fly proportions while ensuring durability.

Functional properties of fly tying threads

When choosing a thread, consider:

• breaking strength,
• ability to shape the body and head,
• compatibility with standard spools and bobbin holders.

Most manufacturers use standard spool sizes that fit typical fly tying tools.

Our range includes threads from trusted brands such as Veevus, UTC, Semperfli, Troutline and selected Hends series.

Frequently Asked Questions

Is a thicker thread always better?

No. A thread that is too thick may distort the proportions of small flies. Thread size should match the hook size and the type of pattern.

What is the difference between 8/0 and 70D?

These are two different sizing systems. 8/0 is a traditional fly tying size designation, while Denier (D) refers to the thickness and weight of the fiber.

When should I use GSP thread?

GSP thread is ideal for patterns that require high tension and strong compression, such as deer hair heads, large streamers and pike flies.