Fly tying equipment and materials
reference guide. Learn how to tie
flies for fishing and display.


There are many colors and sizes of fly tying thread. Black thread is the most common color used for fly tying. If you only could buy one spool of thread then it would be recommended to start with black 6/0 thread. You can then buy other colors and sizes of thread as needed. The average fly tyer will have a selection of several colors and sizes. We have 30 - 40 different colors and sizes of fly tying thread, but most of the time will use black.

The size and style of fly will dictate what thread you will use. Normally you want to use the smallest diameter thread possible to create bodies and heads with less bulk, but not so thin the thread easily breaks. There are other times you want to use heavier thread, such as spinning deer hair or to add extra bulk.

It can be confusing trying to figure out the difference between thread sizes and having multiple standards of measurement does not help. The thread size will be listed on the spool. Fly tying threads are usually sized using the aught or denier measurement system. After using a couple different sizes and brands, you will start to develop personal preferences.

Black 8/0 Thread

The aught measurement system is denoted with a X/O. Common sizes are 3/0, 6/0, 8/0, 12/0, 14/0 and 17/0. The larger the number the smaller diameter of thread. There doesn't seem to be a standardized reference point and actual sizes
can vary between manufactures.

Black 140 Denier Thread

The Denier is more straight forward. The higher the denier number the larger diameter of the thread. Common sizes 40, 70, 140, 210, and 280. Denier is determined by weight/ grams per 9,000 meters More fly tying thread manufactures are starting to use the denier standard and while not perfect, is more accurate and easier to understand than the aught system. The problem with the denier system is that depending on what material the thread is made of will affect the weight. Nylon, polyester, silk, ect., have different mass compared to each other.

Black and Tan 14/0 Thread
This thread has a very small diameter for
less bulk when tying extra small flies. It
is easy to break and will be difficult for
beginners to use. With experience you
will get a feel of the tension and stress
that can be applied to the thread when
tying a fly.

There are no measurements included for the tensile strength of fly tying thread and these are just some thoughts on the subject. Tensile strength would determine how strong the thread actually is by how much stress can be applied. The yield strength of nylon is 45 MPa compared to silk which is higher for approximately the same diameter. There are many factors that can affect the tensile strength including temperature, age of materials and manufacturing process. Most fly tying threads have tensile strengths between 5-10 pounds and Kevlar is rated at 35 pounds. Will be posting some results from our personal at home tensile strength tests after doing a more detailed analyst.

When tying a fly it should be noted that when initially applying pressure on the thread can more than double the tensile load. For instance if you swiftly apply pressure it will more likely break the thread than if slowly applying the same pressure.

Fire Orange 6/0 Thread

There is a wide spectrum of thread colors available. Each brand will have different shades and color range. Most fly tying shops carry a wide range of colors.

There are advantages and disadvantages when using waxed thread. Most waxed threads use a paraffin or rosin based wax.
Advantages to using waxed thread include better grip of materials and dubbing. Wax also helps prevent the thread from fraying and adds lubrication when feeding through the bobbin tube.
Disadvantages of using waxed thread are that it will clog the bobbin and add bulk to the fly.

If using waxed thread it will prevent water based varnish from penetrating the thread wraps. You will have to use solvent or alcohol based varnish in order to penetrate the thread.

When using a non-waxed thread you can always add wax if needed, such as for dubbing purposes. There are many brands and formulations of fly tying wax available. Some are sold in small cubes or blocks and others in tubes. General purpose wax will be firmer than dubbing wax which is softer and more sticky.

Kevlar Thread
Kevlar is very strong and used in applications
such as spinning deer hair. It is recommended
to use an old pair of scissors when cutting
Kevlar as it will damage or dull the blades.
It is also recommended to use a dedicated
bobbin with Kevlar thread, because it can
score the tube and if used with regular fly
tying thread could cause it to fray or break.

More detailed description and uses of Kevlar Thread

The material used to manufacture the thread will effect it's strength. Common materials include nylon, polyester, silk, polyethylene and Kevlar.

General purpose fly tying threads are usually made of nylon or polyester. Nylon has more stretch and polyester is usually a little stronger. There are different opinions as to the best threads and after using different brands, will have to make up your own mind. Most fly tyers probably won't notice the difference between polyester and nylon thread.

Kevlar fly tying thread is extra strong and can be used when spinning deer hair or other applications that might require the extra tensile strength, such as some bass or saltwater flies.

Silk thread was commonly used by historic fly tiers, but is not used as often with modern flies. While it is more expensive, silk thread makes beautiful bodies and tags as seen on Classic Atlantic Salmon Flies and display quality works of art. It is easy to find suppliers of fly tying silk thread with a simple Internet search. Most fly shops don't keep silk thread in stock, but they should be able to place an order.

Most threads are made by twisting two or more fibers. Threads made in the USA generally have a left twist. One of the secrets of fly tying is controlling the twist of the thread. As you wrap the thread around the hook the twist of the thread will tighten. Spinning the bobbin counter-clockwise will loosen the twist of the thread and cause it to flatten out when wrapped around the hook shank.

There are times you will want the thread flattened out. Flattened thread will cover more area for a smoother body with less bulk. Flat thread is also less likely to cut fragile materials such as foam. If applying dubbing with the split thread method, then it will need to be flattened out first.

The advantage of tightening the thread twist is that it will be less likely to fray and offers a better grip or bite when tying on materials. 

Every fly tyer has had the thread break when tying a fly. Breaking the thread is a common problem for the beginner, but can happen to the most expert of fly tyers. While it can be frustrating, usually you can survive this experience and continue construction of the fly by starting new wraps of thread and secure the original thread in position.

There are a several reasons the thread might break when tying a fly. The first reason and most common with beginners is accidentally applying too much tension on the thread.

The bobbin could be the reason the thread is breaking. The first thing to check is the condition of the thread feeder tube. The inside of the tube should be smooth and if you see any nicks or score marks replace the bobbin. Scratches or nicks can fray the thread causing it to break much easier. Ceramic thread feeder tubes are popular because they are more resistant to damage than metal thread feeder tubes. Solid ceramic tubes are more expensive than metal tubes with ceramic tips inserted, but both are effective in preventing damage to the bobbin thread feeder tube.

Bobbin tension could be the problem if the thread seems to break easier than normal. The thread should flow smoothly without undue tension.

Another problem is the initial load tension. Avoid sharp or sudden jerking motions with the thread. With slow and deliberate motions you can apply tension with a minimal initial load factor.

Another common error is to accidentally cut the thread with scissors while in the process of removing other fibers or materials. Almost everybody has made this mistake at one time or another and all you can do is cover your eyes and pretend that it didn't happen. In real life recovery is sometimes possible by starting a new wraps of thread and secure the end of the original thread that had broke, but other times the cut is right against the point where the last material had been tied on,allowing the materials to shift position.

Thread can also be affected by age, temperature, UV rays, moisture and a number of other factors. It can be difficult to determine such factors, but threads bought from a fly shop should not be a problem. We have bought thread that was defective. In one case if you looked closely at the thread, could see areas that looked deteriorated and would break when the slightest pressure was applied.

Fly Tying Bobbin
Fly Tying Bobbin
Used to dispense and control the
flow of thread when tying a fly.

Gel Spun Polyethylene or GSP is a little bit stronger and supple than Kevlar, but is more slippery and may require a drop of super glue to secure in place.

Basic instructions to thread a bobbin


Fly tying equipment and materials
reference guide. Learn how to tie
flies for fishing and display.