Gleipnir

In Norse mythology, Gleipnir (Old Norse for "open one") is the enchanted rope that is tied round Fenrir (as attested in Chapter 34 of the Prose Edda book Gylfaginning).

Myths & Legends
The gods attempted to bind the wolf twice before with large metal chains but both attempts ended with the chains broken beyond repair. They commissioned the dvergar of Svartálfaheimr to forge an unbreakable chain. To create this the the dwarves used six impossible ingredients:
 * The sound of a cat's footfall
 * The beard of a woman
 * The roots of a mountain
 * The sinews of a bear
 * The breath of a fish
 * The spittle of a bird

Therefore, even though Gleipnir is as thin as a silken ribbon, it is stronger than any chain.

Fenrir sensed the gods' deceit and refused to be bound with it unless one of them put his hand in the wolf's mouth. Týr, known for his great wisdom and courage, agreed, and the other gods bound the wolf. After Fenrir had been bound by the gods, he struggled to try to break the rope. When Fenrir found he could not break the ribbon he bit off Týr's hand. As a result of this deed, Týr is called the "Leavings of the Wolf". Gleipnir is said to hold until Ragnarök, when it will break and Fenrir will be free to devour Óðinn and be killed himself by.