Sure Grip Zombie Quad Roller Derby Skate Wheels Black 92A Size MID - 4-Pack : Sure Grip Zombie Quad Roller Derby Skate Wheels - Your Choice of 89A Purple, 92A Black, or 95A Red in LOW MID or MAX wheel sizes! Tired of new wheels not performing like your last set? The Zombie wheel will never have this problem. Zombie wheels feature anodized aluminum hubs for maximum durability and precise feel while maintaining rock solid stability. This allows our unique urethane compounds to deliver all your power to the floor. Choose the Zombie combination that fits your skating style and surface. Zombie Aluminum Core ? Designed in house and manufactured using state of the art machining technology. What makes this different from other aluminum cores? The Zombie core is machined from a solid billet of aluminum, using the same manufacturing processes as they use to make the famous Power Trac racing plates. This increases strength and allows us to machine the hub to a tighter tolerance than any other hub on the market. Creating the perfect fit between bearing and inner core. Cores are then treated with a special anodizing process to increase hub durability and urethane bonding. This technology is unique to the Zombie wheel line. Zombie Insane Urethane ? Specially formulated to our exact specifications that were developed from 75 years in the skate wheel business. What makes this wheel different from the rest? All wheels are poured using a precise time schedule to ensue product quality throughout the range. Typically wheels are poured over time, sometimes days. This can change the characteristic of a wheel poured one day vs. another or even morning vs. afternoon. This timing is what make the Zombie wheel the most unique wheel on the market.