Fences
Green Bandit Wall, Ribbed, 2x1
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), The Wright Residence (tier 4), The Wagner Residence (tier 2), Camp Deucenhalf (tier 1), Mercy Point Camp (tier 1), John & Sons Construction, Outlaw Outlets, Trader Bob, Trader Hugh, Trader Jen, Trader Joel.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.