There are round threads and flat threads. There are single and multi-strand threads. There are threads with texture and threads that stretch. There are even threads that are pre-waxed, and all come in every color of the rainbow. Telling them apart can be a nightmare. Understanding the difference will make picking the right thread for the right fly easy.
In this edition we will talk about the different sizes of threads.
Threads are measured in two main ways in fly tying: Denier and aught:
Denier
Denier is a fixed length measurement. It is the weight in grams of 9000 meters of a given thread. That means, the larger the Denier number, the heavier the thread. So a 210 Denier is a stronger thread than a 140 Denier. We use 210 as our perfect streamer thread and 140 for our larger dry flies.
210 > 140
Aught
The Aught System was created in the 1930's referring to the thickness of Danville threads. In the past, the diameter of thread was measured and noted with a series of zeros. For a reason we couldn't find, the greater the 0's, the smaller the thread size. A thread with six zeros would be noted today as a 6/0 (or 6 aught). That means, the smaller the aught, the larger the thread.
We use 8/0 as our standard dry fly/nymph thread and 16/0 for the smallest and most delicate flies. (The ones that those of us who need bifocals no longer tie without a very large magnifying glass!)
8/0 > 16/0
Of note, aught measurements of today are not necessarily consistent between manufacturers.
COMPARISON
8/0 in relation to Denier would be approximately 70 Denier,