Possible Clues:

• Nautical knot for shortening a rope
• Knot used to take up slack
• Wool producer's skein getting a knot
• Knot used for shortening a rope
• Rope-shortening knot
• PS He has Ken (anag) — rope-shortening knot
• Knot used to shorten a rope temporarily
• Line-shortening knot
• Knot used to shorten lines
• Not, by the sound of it, a stringy leg of mutton