Fences
Green 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 (8 POIs)
Champions Coliseum (tier 5), Beanthere Coffee Company (tier 4), Our Best Moments (tier 2), Mercy Point Camp (tier 1), The Simmons Shanty (tier 1), ParKing Lot, Trader Bob, Trader Jen.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.