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Denier and the "aught" System

In the late 1930's, the Chenille Company created the "aught" (3/0, 6/0, 8/0. etc.) system to indicate the size of thread. This was based on a system where the number or "aught" was the base point adn as the thread became smaller additional zeros were added indicating that the thread was finer. As an example, a thread with zeros (000000) thranslated to a 6/0 thread. As oher thread distributors were born after the early 1960's, they followed the same system which was assigning a standard that does not provide as accurate a measurement for the fly tier as denier.

In 1988, Tom Schymucker of WAPSI Fly, Inc. in Mountain Home, Arkansas introduced a nylon thread simply called 70 UTC ad 140 UTC based on denier which is the method of measuring thread. This is the system that the garment industry uses for thread to sew clothing. Denier is defined as the weight in grams of 9000 meters of nylonk polyester, rayon thread, etc. There is a correlation between denier and breaking strength of nylon and polyester thread, the small the denier number the lower ound/ounce breaking strength of the thread. The one exception to this denier vs. breaking strength rule is the gel spun polyethylene thread is two to three times stronger than nylon or polyester of the same denier.

Thread SizeThread Denier
A or Monocord280

Thread Construction

With the exception of monofilament, fly-tying threads are produced by combining a number of finer filaments. These filaments canbe of different sizes depending on how they were processed. How many, and what size, filaments are used governs the "size" of the thread.


Flat Threads

In what are commonly called "flat" threads, the individual filaments are parallel or have, as a group, only a few twists per foot. They are the little brothers of floss and, like floss, can be difficult to handle with rough fingers. Also, without treatment, flat threads have a tendency to spread out at the wrong time. On the other hand, this property is desirable when tying some patterns.


Round Thread

Give the filaments a few more simple twists per foot (how many depends on the manufacturer) and you have the first "round" thread. Threads with a simple twist resist fraying but can also be easily "flattened." To further assist in keeping the filaments together, some theads are lightly bonded. Such light bonding does not inhibit flattening.



Several strands of a simple-twist thread can be combined in a variety of ways. One way is a rope-twist. This simply twists the several strands together to look like a rope.Obviously, rope-twists are confined to larger thread sizes.

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Thread Materials

Fly-tying threads are made from a number of materials, the most common of which are polyester and nylon.


In general, for the same size, polyester thread is stronger than nylon. Polyester thread is available in a broad range of sizes, colors, and treatments - such as fluorescence.


It comes in several styles - flat, simple twist, and rope-twist - and treatments. Unlike polyester, it isn't normally bonded, and so the flat and simple twist styles easily separate into individual filaments. It is also stretchier than polyester.


Kevlar thread is extremely strong, but more expensive than polyester or nylon. Its major use is in tying large flies and tying with difficult materials. It is impervious to saltwater damage. It is difficult to cut - slide the thread under tension into open scissors blades.

GSP (Gel-spun Polyethylene)

Although more expensive than Kevlar, GSP threads have mostly replaced Kevlar. It is as strong as Kevlar, available in a wider range of colors, and colors. Also, the same strength GSP is smaller in size that Kevlar. Some tiers prefer GSP thread for tying deer-hair patterns. Also, good to use when tying Glo-Balls. To cut GSP be sure the thead is under heavy tension when the scissor blades are closed.


Fine translucent monofilament has a good strength/diameter raito. A slippery surface helps when you want to twist materials around the thread without the thread twisting. Drawbacks include a hard surface that is no help in gripping materials and, because it retains it shape, it builds up rapidly.


Wire can be used as a fly-tying thread. The classic example is Frank Swayer's Pheasant Tail Nymph. Other patterns call for dubbing directly onto wire or creating dubbing brushes with wire cores.

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Wax - No Wax?

The use of wax on tying thread does have advantages. Wax lubricates the thread and helps to prevent abrasion in the bobbin tube. Wax helps to grab materials better as opposed to the slick surface of un-waxed thread. Wax also helps to prevent deterioration of thread over time.

The disadvantages are that some manufactures use a heavy wax that can clog bobbin tubes, and it prevents some water-based head cements from penetrating well. To offset these problems use lightly waxed threads and alcohol-based head cement.

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Thread Brands

Danville is one of the oldest fly-tying thread companies the U.S. In reference to thread size and strengths, they are used as a standard. They also make most of the chenille you see in fly shops, and also sell mylar tinsels and braids. All Danville thread is made of nylon. Spiderweb. This is very thin thread for tying the smallest flies. Finesse and smooth hands are necessary to use it. Available in white.
Flymaster. This is a flat fine thread and is also called Danville 6/0 or in older literature, Herb Howard Prewaxed. Flymaster is a good thread for smaller flies and where low thread buildup is critical. It is probably the most widely used thread in the world and it is the standard to which other fine threads are compared. Waxed or unwaxed; 25 colors.
3/0 Monocord. Monocord has a stiffer feel than other Danville thread. The 3/0 is good for flies larger than #12. It will work for flaring small amounts of hair, such as heads on hoppers. Waxed; 10 colors.
Flat Waxed Nylon. This is a very popular thread for saltwater flies. It has very little twist and it lays very flat. It is strong enough for hair work. The fluorescent colors are bold. Waxed; 15 colors.
Monocord. This is a heavier version of the 3/0. It is typically used for hair work. Flat Waxed Nylon and Flymaster Plus have taken its place in the market. They have better names and colors. Waxed; 10 colors
Flymaster Plus. This is similar to Flat Waxed Nylon, but it has more twist. It is a good thread for hair and large flies. Bold colors. Waxed and unwaxed; 21 colors.
Monofilament. Ultra Fine .004 and Fine .006. Clear and smoke.

Benecchi Benecchi threads Threads are unwaxed polyester with a fair amount of twist. The twist gives it an outer texture that may help hold materials. Benecchi also has a fine GSP thread. The spools come with an end cap to hold the thread when not in use. All of the polyester threads have a similar feel. Benecchi is based in Italy.
12/0. A nice thread for small flies. It spreads out nicely when wrapped on the hook. 20 colors
10/0. A good general purpose thread for flies larger than #18. 20 colors.
8/0. A good thread for larger trout flies, bonefish flies, or flaring hair on smaller flies. 20 colors.

10/0 GSP. A fine strong thread for small flies. It is more floss-like and less stiff than other GSP threads. White.

Gudebrod The American company Gudebrod sells thread for fly tying and rod wrapping, as well as for the general textiles market. They also manufacture dental floss, fly-line backing and almost any filament product you can think of.
I always assumed Gudebrod thread was nylon, but Bob Siegl at Gudebrod informed me they are polyester. Gudebrod thread has more stretch than other polyesters and are a good compromise if you don't like nylon. Gudebrod thread has more wax than most, and is probably the easiest to dub on. All Gudebrod threads are flat.
Gudebrod colors are coded to the Borger Color Guide System, and spools are labeled with the thread color and the BCS number. The bright colors in this brand are very vibrant.
Since Gudebrod is in the sewing business, you can also buy this thread on larger sewing machine spools. To use this thread, you'll have to snap the spool onto a special Gudebrod plastic bobbin, or use a Griffin Multi-thread bobbin (no longer available) which fits larger spools and can be used with all sizes of Gudebrod thread.
Gudebrod also sells Kevlar and mono. The "A" rod wrapping thread can be used for flaring hair. All Gudebrod spools have built-in thread clips to keep the thread from coming off of the spool when not in use.
10/0. A very fine thread for small flies. It is the last step before going to the micro fly threads and will cover most tiers small-fly needs. It has more than twice the strength of smaller threads. 7 colors
8/0. A good thread for small to average trout flies and for larger flies where bulk is an issue. It makes small neat heads on flies. 12 colors
6/0. A thread for flies larger than #14 and for hair work on flies such as Irresistible or making small heads on deceivers. 16 colors.
3/0. A useful thread for hoppers, Muddlers, Woolly Buggers and saltwater flies. 14 colors.
G. A strong thread for hair bass bugs and also good for building heads on big flies. 13 colors.
Kevlar. The original "superthread" used for heavy hair work. 7 colors.
Mono. Available in three sizes in smoke and clear.

Gordon" Gordon Griffith's Gordon Griffith's is a tackle distributor in the U.K. All these threads are made of polyester. The 14/0 and 8/0 are similar to Benecchi thread.
Sheer Ultrafine 14/0. A small-fly thread for nymphs and drys. A good option for big flies such as salmon flies where small heads are desired. Lightly waxed; 11 colors.
Wisp Microfine 8/0. A thread for trout flies #14 and smaller. Waxed or unwaxed; 10 colors.
Cobweb 6/0. This is a two-ply twisted thread. An option for hoppers, ribbing fly bodies, or for building heads on streamers. Waxed or unwaxed; 17 colors.

Wapsi Wapsi isn't a newcomer to fly tying, but has only recently entered the thread market. Wapsi is based in the US, and also distributes many other thread brands. Wapsi Ultra Thread is nylon, and has the appearance of floss. There is almost no twist and it flattens as well as any thread available. It is similar to Danville Flat Waxed Nylon, but available in smaller sizes. It has a shiny finish and the fluorescent colors are brilliant. It is a great substitute for floss. Both sizes are identical in feel and color. It is very easy to make multiple-turn whip finishes, and it creates very smooth heads on flies. Ultra Thread is lightly waxed. Wapsi is the first thread company to actively promote denier thread sizing. Spools are marked with color and size and include a color coded end cap to hold the thread end.
UTC 70. An excellent thread for small flies and low bulk big flies. The spreading nature of the thread makes it easy to tie low-profile flies. 18 colors.
UTC 140. A great thread for flies #14 and larger. Useful for tying flies such as the Madam X, hoppers and Clousers. A good substitute for floss; 18 colors
UTC 280. A nice flat thread for smooth heads on large flies and for tying bulky materials such as hair and wool. It makes excellent tags on steelhead flies; 10 colors.
Mono. Clear and smoke in .004 and .006.

Uni Uni-Products The Canadian company Uni-Products carries the biggest range of spooled fly-tying materials. The company sells thread in a many different sizes and styles. Most of the thread is polyester, but Uni-Products also sells some nylon, kevlar, mono, and GSP threads for different applications. This company does an excellent job of labeling its products. The thread sizing labels won't peel off, and the color information is on them also. Labels in the future will also have denier weights on them. Sizing on GSP threads has already been revamped to reflect denier weights. The 3/0 Uni-Cord is now 7/0 and the Uni-Cord 8/0 now called 12/0. Uni-Products' continuous filament, bonded threads seem proportionally stronger than other polyester threads. The unwaxed 8/0 and 6/0 feel similar to Benecchi and Griffith threads.
17/0 Trico. A fine polyester thread for tying micro flies. Finesse and smooth hands are necessary. Unwaxed; white.
8/0. An excellent thread for small flies and low bulk tying. Continuous polyester filaments are slightly bonded. The texture of the thread helps secure materials. Waxed or unwaxed; 21 colors.
6/0. This is a heavier version of the 8/0. An abrasion-resistant thread. Good for big drys, bead-heads and streamers that require tying in multiple materials. Waxed or unwaxed; 24 colors.
3/0. A flat polyester multifilament thread that works well for covering bulky materials. Used for flies larger than #12. Waxed or unwaxed; 17 colors
A+. A heavier version of the 3/0. It can be used for hair bugs and building bulk on flies. Waxed and unwaxed; 13 colors.
Big Fly Thread,. A heavy, flat, bonded, polyester thread with continous fibers. Good for bass bugs if you desire a non-stretch thread that isn't slippery like GSP or kevlar. Useful for building bulk and covering material on pike and offshore flies. Unwaxed; 10 colors.
1/0 Neon Flo. A very bright fluorescent 2-ply polyester thread. Designed to make bright heads. Also good for thread bodies and ribs. Unwaxed; 6 colors.
2/0 Poly II. A 2-ply polyester thread for those who prefer a traditional round tying thread. Unwaxed; 12 colors
Uni-Cord 7/0. A heavy duty thread for flaring hair, wool, and egg yarn. A great thread to use with large quantities of hair and for marginal hair. Uni-Cord has a nicer finish than some other GSP threads. Unwaxed; 6 colors
Uni-Cord 12/0. A finer version of the Uni-Cord 7/0. A good option when you need superior strength on small flies. Unwaxed; 6 colors Kevlar. Similar in size to other Kevlar, but it has a much softer feel. Natural yellow color.

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Recommended Threads for Fly Tying

Very Small Flies - 18-28

SMALL FLIES -- 10-16

(Streamers, large nymphs and dries, small saltwater patterns)



(N) = nylon, (P) = polyester, (GSP) = Gel Spun Polyethylene, (M) = Monofilament
Recommendations taken from Chris Helm's essay on Threads - "Using Denier to Standardize Tying Threads".

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