Fences
Brown Bandit Wall, Siding, 2x2
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 (11 POIs)
ChemTech Distribution Center (tier 4), Bill Gearz Place (tier 3), Fortified Farm (tier 3), The Johansen Residence (tier 2), Hog Foot Village (tier 1), Hook, Line, & Sinker (tier 1), The Simmons Shanty (tier 1), Fortified Fizz Cola Warehouse, Navezgane Outlets, Trader Jen, Trader Rekt.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.