A Kreitler Alloy Roller system is the "Rolls-Royce" of roller systems - masterfully machined, perfectly balanced, and designed for decades of use. Smooth as the back of razor, the Alloy drums are machined from aircraft-grade 6061 alloy to within two thousandths of concentricity and spin effortless on high-grade ABEC-5 sealed cartridge bearings. Alloy end caps are heavier than the polycarbonate end caps found on the Challenger series. The Alloy end caps create more momentum in the rollers and an increased coasting effect. The difference in weight is more noticeable on the larger drums. While the polycarbonate end caps of the Challenger series are high quality and built to last, the Alloy end caps maintain momentum better and are even longer lasting.