These magnetic tube cord clasps work perfectly for round leather or cloth cords. They hold 4mm round cords, but you can also double over smaller cords inside the tube. I recommend using a strong glue such as E6000 to attach the clasps to the cords.
Comes in individual packages
Made of silver- or gold-plated copper
Dimensions: 18.5mm long (together), 9mm long (separate), 5mm wide