Thread cord halfway through the last link of one end of the jack chain. Bend the cord in half so both ends meet.
Thread both cord ends together through one aluminum sleeve, then slide the sleeve all the way down the cords to create a 1/4-inch loop around the link of jack chain. Glue around sleeve edges to secure and allow to dry.
Thread both cord ends together through the second aluminum sleeve until 1/2 inch of the cords appear through the other side.
Trim one of the cords, and pull the sleeve back over it slightly until the cut end is hidden halfway down inside the sleeve; add glue inside the sleeve to secure the cord. Allow to dry.
Add more glue inside the aluminum sleeve where the cord end is hidden, then thread the remaining cord end through the last link of the other end of the jack chain and insert it into the sleeve to create a second loop to close the necklace. Allow to dry.
28-inch piece of 1/16-inch cotton cable cord
12-inch piece of #16 size brass jack chain
Two 1/16-inch aluminum sleeves
All-purpose clear drying white glue
Your local hardware store should be able to cut a piece of jack chain to size for you; if you have to measure it out yourself from a larger piece, use standard household pliers to bend apart the links to separate the length you need.