Chain

Chains are metallic decoration blocks.

Natural generation
Chains will generate in bastion remnants and sometimes in ruined portals.

Placement
Chains do not require a supporting block to be placed whether it's on the top, next to it or in the bottom, it can exist completely free-standing in mid air and can't be rotated.

From block loot
Chains can be mined using any pickaxe. If mined without a pickaxe, it drops nothing.

Usage
Chains can be used to suspend lanterns (and their soul fire variant) and mob spawners. Mob spawners don't have a chain texture to connect with the chain, instead they generate naturally in bastion remnants. The chain texture connects to the chain of the lantern seamlessly. However, bells cannot be attached to chains, despite the fact that they fit otherwise via and other methods. Chains can be pushed by pistons without being broken. Chains do not connect horizontally.

Breaking
Chains require a pickaxe to be mined, in which case it drops itself. When mined without a pickaxe, it drops nothing. Unlike other metallic blocks, chains can be mined with any pickaxe instead of stone tier and higher.

Trivia

 * Chain is made out of two iron nuggets and one iron ingot, but its blast resistance is actually the same as the block of iron, it seems that the developers tried to make it consistent, even though a chain is smaller than a block of iron.
 * Unlike iron bars or walls, it does not connect horizontally. A solid but not a full block, it allows for many sizes of mobs and players to pass alongside each piece horizontally. When players throw an item, the item can pass alongside it.
 * Despite its name, it cannot be crafted into chainmail armor.
 * Chains is actually using the top texture of the lantern.