Hanging by a thread
Thread, silk, cotton whatever you call it, it is probably the most important part of a fly other than the hook.
Have you ever experimented with different threads early in your fly tying career leading you to choose a favourite thread? I certainly did. Human nature being what it is means we often stick with that same thread through thick and thin and only changing it when we can’t get it anymore. Well I started to wonder what those other threads were like, of course my favourite thread got jealous and we had a bit of an argument along the lines ‘how could you leave me after so long’ which was quickly resolved when I said I was only doing this in the name of science and the Fly Dressers Guild.
Therefore for those with an enquiring mind but don’t want to upset ‘the thread indoors’ do you ever wonder how the different threads compare against each other? What does 70 denier mean and is this the same as 8/0. Does 8/0 thread break with 2lb of pull or 2ozs?
Well I decided to try and pull together a definitive chart. I hope that I have got all of your favourites in here – if not send me details and I’ll add them to the chart. It is not complete, by any stretch of the imagination but it’ll do for now and I’ll add extras if anyone wants to send me a spool of thread to test. I have tried to get the manufacturer specifications for each of the threads and where there are gaps either the manufacturer doesn’t know or isn’t saying! One other thing I also need to point out is that Gudebrod has stopped making fly tying threads and only a few suppliers in the US and UK still sell this – but seeing it is still found in some fly tyers boxes I’ve put it in.
If we are going to make any sense of the comparison table we are going to have to go back to basics with the fundamental questions of what does those strange symbols and language mean on a spool of thread? Well basically they are a notation for the fineness or sheerness of the thread.
The Naught Scale
The first attempt at some sort of thread notation was the ‘naught’ scale. This was based on a system where the number 0 or "naught" was the base point (i.e. the company standard) 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 manufacturers appeared they followed the same system however each company had a different standard for its base point. As more brands became available, the accuracy of the "naught” became pointless unless comparing within the same company. Now it is often I say this but thank goodness for the French as they ‘invented’ the Denier scale.
For those who didn’t know Denier is a measure of the fineness/sheerness of thread. It is based on the number of grams per 9000 metres. Therefore a 70 denier thread weighs 70 grams. Therefore the finest thread has the smallest number.
Of course it couldn’t stay this simple. The international drive for decimalisation and the use of SI units (mm, km, kg instead of inches, miles and pounds) created the Decitex, which is the weight in grams per 10,000 metres and is the officially adopted unit of thread fineness (NB of course it has been adopted by the EU which means that nobody actually uses it but it is here in my table just for completeness).
There is a correlation between denier and breaking strength of nylon and polyester thread. The smaller the denier numbers the lower breaking strain sounds obvious and of course it is – however when you get onto comparing Kevlar and GSP (Gel Spun Polypropylene) threads they are much stronger than their equivalent nylon of polyester threads therefore they can have a higher breaking strain for the same denier.
Fineness or breaking strain of a thread is not the end of the matter, there are other issues such as can the thread be split for dubbing loops?, does the thread lie flat if twisted against the roll of the individual fibres?, how slippery is the thread? and does it grip all materials well? The list goes on – but basically you will need to try the threads to find the ones you like and suits your tying style (just like choosing a rod to match your casting style). Hopefully this table will point you in the right direction to start trying other threads. Good luck if you do!