Scrap Metal (Fallout 3)

Scrap Metal can be traded to various different NPCs located in Fallout 3.

Desired by Walter in Megaton after completing the quest: Fix broken pipes around Megaton. He is located in the Water Purification shack during the day. He provides approx: 10 caps per 1 unit of scrap metal and the Game provides approx: 5 to 10 exp per 1 unit of scrap metal.
 * There is either some pathing issue, or perhaps a scripted event, that may eventually cause Walter to be found dead at the bottom of a slope to the left of the clinic. It may be there's a max number of times you can use him to turn in Scrap Metal before the game kills him off to prevent further turn-ins.  Otherwise, it's likely just a pathing issue that causes him to fall to his death.

Winthrop in Underworld also trades for scrap metal, but he will give Stimpaks or Rad Aways in return, per 5 units.

Protector Casdin of the Brotherhood Outcasts, is a much better option than Winthrop and is located in Fort Independence. He will trade 12x 5.56mm ammo, 1x Stimpak, 1x Rad Away or 2x Frag Grenades per 2 units.

Scrap Metal's additem code is 31944.