Shackle

The Shackle is an Accessory that grants 1 point of Defense for each one equipped. It is dropped by Zombies somewhat rarely, although it's easy to acquire in plentiful amounts if you venture into the wilderness during a Blood Moon and keep killing zombies.

It can be wise to farm this Item from Zombies early on, when Defense is a hard commodity to find, and the Player has no other accessories to fill the slots anyways.

They become obsolete near the end-game, as the player can obtain an Obsidian Skull or Cobalt Shield, which offer 2 defense and, respectively, immunity against burning blocks and knockback.

They can be sold to a Merchant for 3 Silver Coins.