Air Duct 4 Sides
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 (34 POIs)
Don Vittorio Spagetto Residence (tier 4), Flushing Rule Palace (tier 4), Hotel Zombona (tier 4), HSP Logistics (tier 4), Pergola Apartments (tier 4), Pete's Outlet (tier 4), Shotgun Messiah Range (tier 4), Super Shamway (tier 4), Town Hall (tier 4), Wasted Stiff's (tier 4), Buy-N-Go Apartments (tier 3), Regional Paper Company (tier 3), Savage Country (tier 3), Super Savage Country (tier 3), The Grand Forks Estate (tier 3), The Hellenes Residence (tier 3), Crack-A-Book (tier 2), Mo Power Electronics (tier 2), The "Broken Dreams" house (tier 2), The Erickson Residence (tier 2), The Haug Residence (tier 2), Bear-N-Land Coal Mining (tier 1), Pass-N-Gas Store #01 (tier 1), Pass-N-Gas Store #04 (tier 1), The Malone Residence (tier 1), Eye Candy Company, JD Shipping, MeltDowns, Nav Pest Control, Route 66 Restaurant Row, Trader Bob, Wasted Mo Power, Wasted Pass-N-Gas, Willtronics Corner.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.