You're looking at 20 meters (21.8 yards) of extremely heavy duty black polyester thread for leathercraft.
This non-stretchable thread measures 0.8mm (0.03 inches) when uncompressed and has been braided in the same way linen thread has, providing smooth and consistent stitching. Comes in a variety of colours, including black, white and dark brown.
This 1mm thread has been treated with paraffin and synthetic resins (no animal waxes were used). It is best used for most leatherwork, from saddles to bags, to wallets.