The Ultra New Rear Hub features a forged and machined 6061-T6 aluminum alloy body with medium-height flanges. The hubs use hollow axles mated to threading wheel fixing bolts (as opposed to the nutted axles). Hollow axles make conversion to quick release easy. Just remove the bolts and insert QR skewer. All Ultra New hubs come with fixing bolts, but all are QR compatible without axle conversion. The axles are made of cromoly steel, while the fixing bolts are stainless steel for corrosion resistance and high strength. These bolts tighten and loosen with a 6mm hex wrench for convenience.