Fences
Grey Bandit Wall, Siding, 1x4
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)
ChemTech Distribution Center (tier 4), Don Diego Estate (tier 2), Caravan Carousel (tier 1), Hog Foot Village (tier 1), The Simmons Shanty (tier 1), Navezgane Outlets, Old Genrik Plant, Trader Bob.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.