Hard Case: Made of metal or resin, offering excellent rigidity and flexibility. Available in sturdy frame types and lightweight zipper types. Casters: Modern suitcases generally have wheels for easy movement. TSA Lock: Many models are equipped with a lock system that allows airlines to inspect the luggage without damaging it. Expansion Function (Expandable): Some products have a function to increase capacity when you have more luggage. Silent Casters: Casters designed to reduce noise during movement. I lost the key, but it's the type that closes by setting a number, so it's okay even without the key.