Fences
Green 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 (13 POIs)
Champions Coliseum (tier 5), ParKing Garage #2 (tier 4), The Wright Residence (tier 4), Wasted Stiff's (tier 4), Bill Gearz Place (tier 3), Bart's Salvage (tier 2), Camp Carwhal (tier 1), Caravan Carousel (tier 1), Hog Foot Village (tier 1), John & Sons Construction, Trader Bob, 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.