This is a half pound (227g) reel of artificial sinew hand sewing thread. This thread is a modern replacement for sinew or 'catgut' thread, which despite its name, used to be made from the intestines of farm animals, most usually sheep or goat.
Artificial catgut is often used to stitch up historical leathercraft projects and those with an American Western style. It teams up very well with veg tan tooling leather.
This is a large reel, standing 11cm tall (4 1/4") The thread is flat and quite heavy weight. We'd suggest that you use No 2 Needles to stitch this this thread. It's heavily waxed and a yellowy-beige colour.