High quality. 304 stainless steel micro bearings, brass, nylon outer wheel and stainless steel screws. Works great. Shower door slides for showers, massage rooms, bathtubs, whirlpools and even furniture hardware. . Ensure the most comfortable sliding of your door. Suitable glass thickness: 4-6mm. Glass door opening size: 10-12mm. Good purchase, definitely worth it. Pulley bearing capacity, good stability; Small friction coefficient, good mute effect. Package: 4 wheels and 4 screws provided per package. Great replacement and easy to install. Fits different types of showers.