Plumbing
Air Duct Ramp Cap
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 (7 POIs)
Shamway Factory (tier 5), Pete's Outlet (tier 4), Town Hall (tier 4), Regional Paper Company (tier 3), Crack-A-Book (tier 2), Power Distribution Station #2, Wasted Pass-N-Gas.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.