Published Mar 24. 2017 - 6 years ago
Updated or edited Mar 11. 2023

Using Denier to Standardize Fly Tying Thread

It makes sense to have a standardization, which would eliminate much of the confusion that surrounds fly tying thread today.

This article was written in 2006/7, and is published here as a part of Chris Helm's thread articles.
Some of the issues discussed here, spawned the article Fly Tying Thread Blues, and are covered in depth and with newer information in that article.
Measuring thread
Measuring thread
Martin Joergensen

In the summer 2004 issue of Fly Tyer, author Lyle Morgan addressed the question of whether standardizing thread size would help tiers become more effective in producing beautiful and effective flies. It certainly makes sense to have standardization which would eliminate much of the confusion that surrounds fly tying thread today. Based on the fly tier web poll conducted in the same issue as Lyle’s article, voters overwhelmingly agreed ( 252 to 32) that thread should be standardized. The process has begun and over the next few years you will begin to see the denier (pronounced DEN-yer) number listed on most of the spools of the major thread distributors. The denier system of count or weight for silk was introduced in France in 1535. The term is derived for "denarius", a coin from Caesar’s times against which lengths of silk were balanced or weighed.

Manufacturers say

Tom Schmuecker of WAPSI started the denier information process by introducing WAPSI UTC 70 and 140 denier thread in 1998, followed later by 210 and 280 denier nylon thread. His purpose in using the denier number rather than the "aught" rating was to try and subtly suggest that this system was more beneficial to the tier than the "aught" system that had existed for more than seventy years. Denier is also a recognized and accepted standard of measurement among thread manufacturers and the garment industry.

The late Jean-Guy Cote’ of UNI-Products was already putting the denier on a number of his products. He stated, however, " I won’t put the denier on the 8/0 thread until I am sure that all of the other distributors are using the same measurement system to identify the denier of their thread". The successor management is continuing to use the denier rating and I am confident that he will eventually put the denier on the 8/0 spools. Uni already identifies the denier of all their products in a chart which is available to anyone.

Paul Black of Gudebrod stated, "I have already started to put the denier number on the labels of our thread since we do all of our printing in house". Of course, this process may take a year or more to complete given the number of thread sizes (7) and the multitude of colors. These new labels will begin to show up in fly shops gradually as the proprietors order new stock. ( Editors note: In November 2006 Gudebrod discontinued the manufacture and distribution of all fly tying threads. However, good supplies remain with many dealers)

Danville manager, Dan Bezanson, stated, "wherever possible, Danville will include the denier on the spool label." A few labels may not contain the denier due to unavailable space. Danville recently introduced a 140 denier thread that does not have an "aught" designation.

Giorgio Benecchi Products, of Modena, Italy, does not have labels on their spools. However, they do provide this information freely to shops or distributors. In my own shop, I use a rubber stamp to put the denier as well as the "aught" rating on each spool of Benecchi thread.

A little bit of history

Historically the "aught" system began in the late 1930’s . Dan Bezanson said, "Based on the information that has been handed down in the company, Danville Chenille implemented the "aught" system to help standardize fly tying thread. This was based on a system where the number 0 or "aught" was the base point and as the thread became smaller additional zeros were added indicating that the thread was finer. As an example, a thread with six zeros (000000) translated to a 6/0 thread. As other thread distributors came into the market place after the early 1960’s , they followed the same system which was assigning a standard that does not necessarily provide as accurate a measurement for the fly tier as denier.

As more thread distributors and brands became available, the accuracy of the "aught " became muddied.
The aught system has caused much confusion with tyers for many years thus prompting the initiation of the use of denier by WAPSI FLY

When only one distributor existed making some sense of the system wasn’t difficult. Now there are at least seven distributors of thread in what has become a very competitive market. It occurred to me in the mid 1990’s that some of the aught numbers being assigned to some thread was a matter of trying to gain a competitive edge rather than providing accuracy for the fly tying customer. That is precisely what generated the article I coauthored with Bill Merg in the summer 1996 issue of Fly Tyer entitled "Testing the Ties That Bind" The focus of this article was on a number of aspects of thread but emphasized breaking strength and thickness.


Denier is defined as the weight in grams of 9000 meters of nylon, polyester, rayon thread, etc. There is a correlation between denier and breaking strength of nylon and polyester thread. The smaller the denier number the lower pound/ounce breaking strength of the thread. At the present time, about the smallest denier nylon or polyester for fly tying thread is 40, which would be used for tying midges. The one exception to this denier vs. breaking strength rule is that gel spun polyethylene thread is two to three times stronger than nylon or polyester thread of the same denier.

Denier is only one factor the tier should take into consideration when selecting a thread. The type of material of which the thread is constructed should be considered, whether the thread is a continuous filament, simple twist, bonded, or a rope type. Nylon has about 25% stretch, polyester around 15% stretch, and gel spun only 3% stretch. The type of material being used on the fly as well as the appearance desired also has to be considered. It is important to experiment with all of the various threads available to gain a complete understanding of the pros and cons of each.

Bill Merg conducted the tests on 15 threads that have become available in the past several years.
All of the other data listed in the chart (see next two pages) is from the 1996 test results. He used the same methodology in testing the various new threads that have become available in the past few years as the tests conducted for the thread listed in the 1996 article entitled "Testing the Ties That Bind" that is mentioned above. On all of the tests conducted in 1995, the various brands showed remarkable consistency in thickness throughout the spool. That was not the case in a number of the threads recently entering the marketplace. Those that showed slight variation in thickness included: (variation shown) WAPSI 210 (.008), WAPSI 280 (.005), Danville 140 (.006), Roman Moser Power Silk 6/0 (.0012). Keep in mind that one spool was randomly selected and used for these tests.

Another thread article by Ed Engle in the Spring 2000 issue of Fly Tyer entitled "Hanging by a Thread" compares twelve different threads for tying small flies. Then he rates the threads in a manner similar to how Consumer Reports evaluates products. This same article appears in Ed’s book Tying Small Flies. Ed describes the qualities of twelve threads and discusses the characteristics of each.

Darrel Martin wrote an excellent article on thread in the March/April 2000 of Fly Rod and Reel entitled "A Thread of An Idea". He discusses silk thread and its history along with numerous facts about thread sizing, characteristics of the each material used in thread. He also comments on thread pressure applied when tying and characteristics of waxed thread.

Matching the thread to the size of the fly and the material being used is extremely important in achieving both functional and aesthetically pleasing flies. The more a tier understands about all the materials used in tying the fly the more efficient and effective fly tier he or she will become.


Editor's note.: Data from this table and many other sources was compiled into this larger and updated Fly Tying Thread Table

Thread Brand Aught Size Material Denier Breaking Strength Thickness (.000)
UNI Caenis N/A mono 20 3 ozs. 1.7
Gudebrod * 10/0 polyester 45 9 ozs. 1.0
UNI 17/0 nylon 40 5 ozs. 2.0
Danville Spiderweb N/A mono 30 5 ozs. 2.0
Roman Moser Power Silk 8/0 gel spun 55 2 lbs. 6 ozs. 1.3
WAPSI 50 GSP N/A gel spun 50 2 lbs. 5 ozs 0.8
UNI Cord 12/0 gel spun 50 2 lbs. 7 ozs. 0.9
Benecchi Ultra Strong N/A gel spun 50 2 lbs. 6 ozs. 1.3
Benecchi Ghost N/A mono 60 11 ozs. 3.0
Gudebrod * 10/0 mono 50 2 lbs. 11 ozs. 6.0
Gudebrod * 8/0 polyester 67 15 ozs. 1.8
Benecchi 12/0 polyester 70 15 ozs. 1.9
Gordon Griffith Shear 14/0 polyester 72 10 ozs. 1.8
Gudebrod * GX1 gel spun 70 7 lbs. 1 oz. 1.1
Danville 6/0 nylon 70 11 ozs. 1.5
UNI 8/0 polyester 72 15 ozs. 2.0
WAPSI UTC 70 N/A nylon 70 13 ozs 1.1
Gordon Griffith Wisp 8/0 polyester 108 15 ozs. 2.2
Gudebrod * 6/0 polyester 143 1 lb. 15 ozs. 2.3
Benecchi 10/0 polyester 120 1 lb. 6 ozs. 2.0
Danville Monocord 3/0 nylon 116 1 lb. 10 ozs. 2.6
Uni 6/0 nylon 135 1 lb. 13 ozs. 2.9
Wapsi UTC 140 N/A nylon 140 2 lbs. 12 ozs. 1.6
UNI Cord 7/0 gel spun 100 5 lbs. 9 ozs. 1.4
Wapsi GSP 100 N/A gel spun 100 6 lbs. 15 ozs. 1.2
Gordon Griffith Cobweb 2 N/A polyester 134 4 lbs. 3 ozs. 4.1
Gudebrod GX2* N/A gel spun 130 6 lbs. 8 ozs. 2.0
Roman Moser Power Silk 6/0 gel spun 110 4 lbs. 8 ozs. 1.3
Gudebrod * 6/0 mono 143 2 lbs. 11 ozs. 6.0
Danville Flat-Waxed Nylon N/A nylon 210 2 lbs. 14 ozs. 2.0
Danville Fly-Master Plus N/A nylon 210 3 lbs. 2.8
Uni 210 N/A nylon 210 3 lbs. 3 ozs. 2.0
Gudebrod * 3/0 polyester 176 2 lbs. 6 ozs. 4.0
WAPSI UTC 210 N/A nylon 210 3 lbs. 5 ozs. 3.2
Gudebrod G * N/A mono 210 3 lbs. 7 ozs. 7.0
Gudebrod G * N/A polyester 330 3 lbs. 11 ozs. 3.5
UNI Big Fly Thread N/A nylon 440 5 lbs. 4 ozs. 3.5
WAPSI UTC 280 N/A nylon 280 3 lbs. 14 ozs. 2.7

* No longer produced


Log in or register to pre-fill name on comments, add videos, user pictures and more.
Read more about why you should register.

Since you got this far …

The GFF money box

… I have a small favor to ask.

Long story short

Support the Global FlyFisher through several different channels, including PayPal.

Long story longer

The Global FlyFisher has been online since the mid-90's and has been free to access for everybody since day one – and will stay free for as long as I run it.
But that doesn't mean that it's free to run.
It costs money to drive a large site like this.

See more details about what you can do to help in this blog post.