Griffin Bead Cord #6 Black is perfect for knotting pearls and beads:

This natural 100% silk cord is used for knotting Swarovski Pearls, Czech Pearls, glass beads and gemstones. Each card has an attached needle which saves you threading time. Griffin thread is very strong so doubling it is unnecessary. 

Black Griffin Bead Cord specifications:

• Product: bead cord
• Color: black
• Material: natural silk
• Country: Germany
• Size: No.4 (0.70 mm)
• Quantity: sold on cards of 2 meters 
• Other info.: needle enclosed