The Magnetic Tray is a small metal pan useful for storing loose Bolts the player accumulates. They're not strictly necessary to own, but are helpful to have given the large number of bolts on the Konig.
55 bolts of any size and color can be collected on the tray at once. Any bolts brought near the tray will automatically be picked up; if a large pile of bolts needs to be picked up at once, the tray can be moved over them. To remove individual bolts from the tray, hover the cursor over the one that's wished to be picked up, and click the Right Mouse Button. To remove all bolts from a tray, equip it in a hand, and press the Right Mouse Button.
Kali-Gas and Roger Pièces D'Autos both stock one Magnetic Tray per day, and it sells for $24.99.