Fences
White 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 (9 POIs)
ChemTech Distribution Center (tier 4), Bill Gearz Place (tier 3), Bart's Salvage (tier 2), Don Diego Estate (tier 2), Camp Carwhal (tier 1), The Simmons Shanty (tier 1), Old Genrik Plant, Trader Joel, Trader Rekt.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.