Junk items refer to the miscellaneous clutter found scattered all over the Commonwealth - toys, housewares, garbage, tools - which the Sole Survivor can collect. Junk items are found in their own inventory section in the Pip-Boy. They cannot be equipped, consumed, or interacted with by themselves like weapons or food, although they can be dropped or sold to vendors. Their primary use is in crafting, either as ingredients for more useful items (weapons, armor, chems, mods, settlement buildings, etc.), or for breaking down into their raw components. After accessing the inventory on a workbench or crafting station at a player character owned settlement, all junk items can be automatically transferred into the workbench and are available for crafting at the settlement, as well as all settlements connected to it via a supply line. Junk items can also be automatically transferred into non-player character owned crafting stations, but they will not be shared between the crafting stations in the area.
All junk items consist of one or more "components", a general term for the materials that make up each junk item. When crafting anything out of junk, the most readily available junk is broken down to its base components, and whatever ingredients needed for the recipe are consumed to make the crafted item. Any components not used are stored in either the player's inventory or the settlement workbench, depending on where the player is crafting and where they are storing their junk. There are 31 base components total, that cannot be broken down further into anything else.
Although some instances of the following items exist in the game world, they are more commonly obtained by scrapping other items. Additionally, shipments providing larger quantities can be bought from several vendors and are weightless.
When scrapping other junk items, you will always receive the components specified. However, when scrapping other items such as...
...you will only receive a fraction of the components which were originally used to craft the item. The types and amounts of components received in these cases is determined by two factors: rarity and scrap scalar.
Rarity has four possible values:
Common: these components are always received.
Uncommon: Scrapper rank 1 is required to receive these components.
Rare: Scrapper rank 2 is required to receive these components.
Zero yield: these components are never received - only applies to adhesive and oil.
Additionally, the original amount of components used to craft the item is multiplied by the scrap scalar, rounding down, when determining the amount of components received.
* Concrete shipment also has a shipment of 200 with ID xx000e80
The unit price of a component, when bought as a shipment, is several times its "base" unit price, sometimes even overpricing the value of a simple source item containing the component. Also, the game does not offer any rebate for large shipments (= no quantity rebate). Therefore, it is not necessary to spare money waiting the opportunity for buying big shipments over small ones. E.g: 2 shipments of 100 concrete yield the same overall price as a single shipment of 200. Buying small shipments also allows building defenses gradually for settlements that are not yet connected between each other, and at a lower cost.
The concrete, steel and wood components constitute the 3 base building components for all the major craftable structures in the settlements (e.g. floors, walls, roofs, stairs). Their values, although claimed to be all 1, are respectively 1, 2, and 3 when considering their respective shipments. For this reason, the cost for building each craftable structure can vary largely, and can affect or determine which structure is favored over the others, especially when the amount of money (caps) is currently limited and... there is an hurry for building up the defenses for a given settlement.