A chain was a series of linked metal loops used for various purposes.
When Sub-commander T'Pol suggested to use stun grenades, detonate them, and use both shuttlepods to bring the Novans back to Enterprise NX-01, Captain Jonathan Archer asked her what to do then with the Novans – put them in chains? T'Pol then stated that Mister Reed would devise appropriate restraints. This suggestion was dismissed by Archer as Enterprise was no slave ship. (ENT: "Terra Nova")