Hi all,
The thickness of an Irish linen thread is not dependent on the numbers of ply. It is the other number, in your example from Hollander's: 18, that is deciding the thickness. I once asked the Linen museum in Lisburn about these numbers relation to the thickness of a linen thread and got this answer:
"Let us take the example of Barbours 12/3.
3 is the 3 ply (a ply is a single thread)
12 is the thickness (lea) and 200 is a finer one. The numbers are related to the weight in lbs (pounds) of a fixed length. This has been a standard form of measure for linen yarn in Ireland (and Scotland) since the 18th century.
In order to raise the quality of production by standardisation of hand spun yarn to a specific measure, the yarn was reeled on a wheel to a specific number of turns. A full reel of 120 turns was 300 yards and was 1 lea. A common quality or weight was a 12 lea which was equal to 1 hank to the lb. (pound). This meant that 12 x 300 yards weighed 1 lb. A higher number multiplied by 300 yards and still equal to 1 lb means a much finer yarn which would weave into a much finer fabric.
A 200 lea thickness weighing 1 lb would thus be a much finer thread. These measures have continued even in machine production times."
So the higher thickness number, the finer thread.
I have tried several types of linen thread on my fletchings;
* 40/3 and finer looks nice and will not make spaces between the barbs of the feather, but on the other hand it won't hold more than 30 shots before it breaks. In these tests I only had bees wax on the thread, so I suppose that it will hold longer if you put on a coat of varnish or glue.
*12/2 and thicker thread will definitely look a bit heavy. They will last, and they will give you the occasional "burn"...
*18/3, is what I used on my last arrows, see "How do I fletch a Soar's battle shaft". This is something in between, and a good substitute if you, as I, have not found a good silk thread yet.
