Psalms 149:8

To bind their kings with chains, and their nobles with fetters of iron;

The iron fetters are a picture of binding. That binding portrays Satan's power to take control of minds. By that control he keeps people from doing God's work.

The binding belongs to the judgment the saints share with Jesus during the thousand years. After entering the city, the saints judge the wicked dead according to their deeds. That judgment records what each will receive when the sentence is carried out.