PC material makes the luggage more durable. lighter and impact-resistant. 21" is best for carry on. 25" & 29" expands 20% for more spaces.TSA lock allows only customs agents to inspect your luggage without damaging the lock and protects your stuffs in luggage and privacy more better. Simply set the combination. No keys are required.Adjustable & sturdy ergonomic 3-step telescoping handle allows you to maneuver in tight spaces and provide effortless movement. Smooth ups and downs for more comfortable carrying.360° Double spinner wheels: Mute. strong bearing. effortless maneuverability.Two hooks (25" 29" ) can hang your computer bag. backpack. hat. etc.. to help you relieve fatigue during your journey.