This is the heaviest Londonderry flax linen thread that Colophon sells. Though comparable in thickness and strength to 12/3 Colophon’s Best, this softer 5-ply thread causes less swelling (allows for greater compression) during sewing. Great for any sewing application where extra strength is needed. Sold unwaxed in 70-meter spools. Available in Ash Gray, Beige, White, and Ivory. 

Unsure which thread you need? Sample cards can be found here. 

If you’re curious to know more about number system used to describe thread sizes, check out this post by book conservator and toolmaker Jeff Peachey.