Fences
Orange Bandit Wall, Siding, 2x2
While not as sturdy as solid concrete, iron constructions have high structural integrity, requiring fewer support pillars.
Harvest drops
Iron× 17
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (75% of the time) where it lands.
Where to find (3 POIs)
John & Sons Construction, Trader Bob, Trader Jen.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.