When it comes to training indoors, the Kreitler Alloy 4.5 Rollers are without equal in improving your spin, balance and form. Kreitler's whisper quiet and silky smooth rollers are the choice of those in the know. 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 Alloy 4.5 Rollers features 4.5 inch alloy drums with alloy 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.