Fences

Fences serve as a wall, but cannot be used for housing. More than four fences placed in a row will render housing invalid. Unlike other walls, it doesn't appear to stop mushrooms/flowers from spawning.

A Metal Fence can be converted back to Iron Bars (but not Lead Bars) at an anvil; this may be unintended. Due to this, crafting and un-crafting this item repeatedly can be used to convert Lead Bars into Iron Bars.