Fences
White Bandit Wall, Ribbed, 3x2
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 (9 POIs)
ChemTech Distribution Center (tier 4), The Wright Residence (tier 4), Bill Gearz Place (tier 3), The Animal Hoarder (tier 2), The Wagner Residence (tier 2), Hog Foot Village (tier 1), Golden Acres Farm, The Shed, Trader Rekt.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.