Chainlinks
Chainlinks are used to repair damaged Chainmail Armor.
Obtaining
Mob loot
Chainlinks are dropped by armored zombies, yielding 0-2 chainlinks.
Spawner loot
One can obtain chainlinks by mining an armored zombie spawner with any pickaxe besides gold, yielding 24 chainlinks.
Crafting
Chainlinks can be crafted by putting any piece of chainmail Armor into a workbench, regardless of durability.
Usage
Repairing
Chainlinks can be used to repair chainmail armor by crafting a chainlink with it. The more chainlinks used to repair the armor, the more durability it receives.