Hope Pro 5 Rear Hub Sram XD XDR Free Hub Bearings. SRAM XD XDR. Spec: GCR15 high carbon chromium bearings steel is standard material or precision C3 bearings. Lubrication : Bearings are supplied with low noise bearing grease thickened by lithium and calcium 12 - hydroxystearate,, made from deeply refined mineral oil with rust inhibitors and anti oxidants.