Scrap metal is a type of rubble that is abundant throughout the biomes of Deepworld. Although it generates in different shapes (some of which can be 2 blocks tall), once you mine it and place it, it is always 1x1 block in size. Scrap metal has varying degrees of collision for players (naturally-generated scrap metal has collision; placed scrap metal does not), but always has full collision for mobs. It does not hold liquids or stop rain. It is unique in that any player can mine it, even when it is in a protected world or under a player protector.
To see the inventory icons for the different sorts of scrap metal, go to their individual pages:
How to Obtain
If you mine a decayed metal block, you'll get scrap metal of the appropriate type.
Scrap metal cannot be crafted, but you can trade for it in a market world.
How to Use
Scrap metal is used in a few crafting recipes, and can be recycled into usable metal blocks at a recycler. Other than that, due to its inability to be protected, it's only useful in temporary ways. You can place it, but like most other forms of rubble, it can be mined even if you put a protector on it.