Proprietary Quadro spherical 4-wheel system provides smooth multi-directional rolling Premium polycarbonate shell with matte-finish, scratch-resistant texture to protect valuable contents TSA approved zipper combination lock Multi-stage trolley handle Fuzion zippers by YKK with woven-in teeth provide 5X the abrasion resistance over the traditional sewn-in teeth in a low-profile design The Quadro 42-liter Hardcase is a strong, secure, and carry-on compliant piece of luggage we can take to any country. A polycarbonate shell feels bulletproof so we can worry less about the contents inside. And to add to that worry-free feel, a built-in zipper lock keeps what's inside locked away from the world. We like the multi-directional wheel design that lets us push it in any direction.