Plumbing
Air Duct Half Ramp End
While not as sturdy as solid concrete, iron constructions have high structural integrity, requiring fewer support pillars.
Harvest drops
Iron× 10
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (60% of the time) where it lands.
Where to find (12 POIs)
Hybrid Mining (tier 5), Super Shamway (tier 4), Town Hall (tier 4), Downtown MeltDowns (tier 3), Jack's Lumber Mill (tier 3), Super Savage Country (tier 3), NEW Mamma Pizza (tier 2), Pass-N-Gas Store #01 (tier 1), Box Factory, Figaro Square, Gray View Apartments, MeltDowns.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.