6000 yards in a spool.
Tex 40 is generally considered a medium-weight for sewing thread (versus very fine or heavy duty). Tex 40 is good for many general sewing uses — garments, mid-weight fabrics — but may be light for heavy canvas/leather/industrial.
Thicker thread often needs larger needle, adjusted tension. If you use a heavy material and a too-fine thread, you might get skipped stitches or thread breakage.