Originally made to counterbalance sash windows. Sash Cords were made of natural jute but they were sometimes waxed to help prevent rot. The stiff waxed type was not suitable for stage use. Years ago there wasn't much choice when it came to small cords and jute sash was very popular. Then Black Cotton "Sash" arrived to fill a need for a black small cord. Recently pure black polyester "sash" is readily available. Polyester is much stronger than jute and less stretchy than cotton. It will not rot but it is more expensive. Matt black polyester sash is listed on page 2.33. The 6mm size (ROP120) is the equivalent of No4 and the 8mm size (ROP122A) is the equivalent of No6. So now there's a choice!
Natural Jute Sash Cord Normally used for throw line cleating. An economical general purpose cord for tying off.