Nuts and Bolts are used to craft several previous vaulted items, such as the Lever Action Shotgun. You need 1x Nuts and Bolts to craft most of the unvaulted weapons that cannot be found elsewhere.
Unlike Mechanical Parts, Nuts and Bolts aren’t found by hitting cars and other vehicles. Instead, you have to find them within red Toolboxes, like you see below.
They are similar to Ammo Boxes but are much, much rarer. We only found one across five or so matches. You only get 1x Nuts and Bolts per toolbox, so you should realistically only expect to be able to find one or two in total across a whole match.
If you have a Recon Scanner, the weapon will highlight any nearby red toolboxes when you fire its projectile.