When it comes to training indoors, the Kreitler Challenger 4.5 Rollers are without equal in improving your spin, balance and form. The Challenger 4.5 Rollers use the same 4.5 inch machined aluminum drum cylinder as the Alloy 4.5 Rollers, but use Poly end caps for a more economical option. Kreitler drums are made from high quality aluminum, lathe-turned to within .002" for smoothness, and anodized for a long-lasting finish. They spin virtually without resistant on instrument quality bearings. The Kreitler Challenger 4.5 Rollers features 4.5 inch alloy drums with polycarbonite end caps and 15 inch roller frame width. The Kreitler Killer Kool Headwind Fan (sold separately) allows you to add resistance to the rollers. Lifetime warranty.