Tarp Fence Sagging Red
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 (15 POIs)
Butcher Pete's (tier 4), Doominium Tower (tier 4), NDC Checkpoint One (tier 4), Atlas Metal Company (tier 3), Greg's Motel (tier 3), Treats Terrace (tier 2), Oskar's Dumpster (tier 1), Pass-N-Gas Store #01 (tier 1), The Book Barn (tier 1), The Roland Residence (tier 1), The Smokehouse (tier 1), Corona Wipes Billboard, Industrial Demolition Site, Junkin, Mini Market.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.