We all do those jobs with small parts where there's a run away spring, screw or clip that is easily lost. These trays are thick walled so rugged and designed to hold all of those parts safely together as you dismantle. It can be a lock to re-pin, firearm, side arm, knife, or anything that can have easily lost parts that roll.
You can even take it in your luggage for change and keys in a hotel. Keep it all together so its easy to pick up and remember.
Size is 6" x 4"