Our kit includes 8 shower door rollers (4 upper and 4 lower twin rollers); each roller measures 25 mm in diameter; they fit windows with a thickness of 4 to 6 mm and weigh 42 to 45 grams. Reliable material Each shower door roller is made of solid zinc alloy with a durable chrome coating; the wheels are made of durable plastic; all materials are high-end, corrosion and rust resistant and will not crack or split over time. Quick assembly These shower door rollers are quick and easy to install; the bottom rollers have a spring-loaded button on the top to differentiate them; once installed, our rollers allow your glass shower door to slide smoothly.