Ilterindi were the great fetters made to hold Melko (Melkor) in the earlier forms of the legendarium.
They combined with the chain Angaino and Vorotemnar, the manacles were to hold Melko indefinitely.
History
Ilterindi were made by the Vala Aulë out of the metal Tilkal. When Tulkas had finally subdued Melko, Aulë set the Ilterindi on each of his ankles.[1][2]