The root of the problem of nailing down the exact diameter probably lies in the fact that it was originally an industrial product made to bind things. Anything and everything. It wasn't meant to meet a particular exacting standard (as far as I know of). This product just so happened to make its way into Danish modern chair production because of a number of reasons.
Despite this, as far as I have experienced, there is an amazing consistency in size from roll to roll and from different suppliers, though I now primarily source it from one company in the US.
I used to use a rough figure of 7 cord widths per inch. This works for anything less than 3" but anymore than that and it becomes clear a more accurate measurement is needed. Here is where it gets ugly. There is no easy measurement that fits. It doesn't even make a clean round number in metric.
It is somewhere between 1/8" and 9/64". Or somewhere between 3.5mm and 3.6mm. I have landed on the figure of 0.13875" or 3.52425mm. It is close to 31/32" for 7 cords which works ok for figuring the nail locations on a 5/2 cord layout.
Since this figure is awkward to work with in the shop for laying out cord and nail locations I made a ruler for simplifying the process and of course want to share it with all of you.
Don't be confused by all the little blocks. There are instructions on how to make a ruler with the print out. It is designed so that you can create a two sided rule and be able to pair it with the different standard ratios of cord layout used on most danish modern chairs.
It is sized for printing on standard 8.5 x 11 paper. The rule is 10" long and can be made longer by butting pieces end to end. I suggest using some clear plastic tape to laminate it with to create a simple flexible rule. Choose from several different measuring ratios, such as, 5/2, 4/2, 2/2, and a basic 1/1. I paired most of these with the option to have a 1" scale on the reverse side.
Hope this makes your shop life a little easier. BTW I decided to make this after weaving a CH25 pair that I recently made. I will post some photos on that since I know many have questions on how it is done.
CLICK HERE TO GO TO THE DOWNLOAD PAGE. (Click on the download button in the upper right corner of the new page to begin download.) NOTE: THE DOCUMENT IN THE LINK DISPLAYS INCORRECTLY BUT THE DOWNLOADED IS JUST FINE.
NOTE: The plans are in PDF format. If you don't have a PDF reader Adobe Acrobat is a free software that will make it viewable and printable. Make sure where ever you print it that the "scale" is set to 100% or the measurements won't be accurate on the print. You may need to unselect "fit to page" when printing.
If I made any errors anywhere in the plans please let me know so I can update them.