Fly Tying Thread, Denier, Ought Sizes, Thread Sizing and Breaking Strains
Monday, 6 October 2014 | Admin
Thread diameters were created in the 1930s. In the fly tyers have been using 6/0, 8/0, 12/0 fly tying threads plus many others, however in 1988 WAPSI fly introduced a thread called 70 UTC and 140 UTC for their UTC threads based on Denier sizing. There has been confusion since!
Denier is defined as the weight in grammes of 9000 meters of polyester, nylon or rayon threads. There is also now for most threads a correlation between the breaking strain on most threads for examply typically a 70 denier thread will be stronger than a 30 denier thread. HOWEVER, GSP or Gel Spun Polyethylene is an exception to the rule as GSP can be from 3 to 9 times stronger than nylon or polyester of the same denier. For example Semperfli Nano Silk 30 Denier has a breaking strain of 1,140gm / 40 ounces yet the thicker Uni 17/0 or 40 denier thread made from nylon has a breaking strain of 140gm / 5oz, Nano Silk over 8 times stronger. This gets further confusing as even GSP's are not the same, for example Veevus 12/0 GSP breaks has a breaking strain of 530gm compared to Nano Silk 12/0's 1900 gm, 3.6 times stronger due to its special makeup! Presently, there are threads available, which although identical, are labeled with vastly different N/0 size
So the best we can hope for as fly tyers is a guide to the thread diameter so that we can guage the size of head that will be created using a thread. Of course a twisted thread will be thicker than an untwisted thread which will lay flatter on the hook.
Nylon has about 25% stretch, polyester around 15% stretch, and gel spun only 3% stretch
Most threads are made by twisting multiple plies to make the required size. Left Twist (or Z-Twist) thread is twisted to the left and works with almost all single-needle machines. Right Twist (or S-Twist) thread is twisted to the right and is used with some U.S. double-needle machines.
Approx Thread Breaking Strains vs Aught Sizes
Fly Tying Threads By Breaking Strain