Angainor
From Tolkien Gateway
Angainor was the chain used to contain Melkor (who was later known as Morgoth) in the Halls of Mandos. It was constructed by the Vala Aulë and held Melkor for three ages (around 2,900 solar years).[1] At the end of the First Age, Melkor was again bound by Angainor, and his iron crown was made into a collar.[2]
Etymology
The name Angainor contains Quenya anga "iron".[source?]