This thread is called artificial sinew and is a rot-proof replacement for natural animal sinew.
Artificial sinew is often used to stitch up historical style leathercraft projects and those with an American Western style. It teams up very well with veg tan tooling leather.
This is an 18 metre (20 yard) reel. We suggest that you use No 2 size Needles to stitch with this thread. It's heavily waxed and pale yellow in colour.
We also sell this thread is a very economical 356 metre reel, which can be found here.