Iron bars are used in numerous crafting recipes.
Iron Bars are grey in color and can be obtained from Zombies in Hell, high level Zombies, and Skeletons or from a Dragon's loot. They craft some great items and are extremely helpful. Iron bars aren't very often obtained other than by mining 2 iron ores, and aren't very frequent anywhere before the Mountain biome. Because of this, they are advised to be stockpiled in a crate at your main base. Iron bars are needed for Gold Tools and Gold Guns.