Fences
Grey Bandit Wall, Siding, 3x3
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 (8 POIs)
Grover High (tier 5), Two Bit Tower (tier 5), U.S. Army Post #7 (tier 5), Bill Gearz Place (tier 3), Caravan Carousel (tier 1), Old Genrik Plant, ParKing Lot, Trader Rekt.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.