The fsa os99csi ud carbon stem the 99 csi is 3 d forged and cnc machined from al2014 before a uni directional carbon weave skin applied through the carbon structural integration process to further reduce weight the os 99 uses a 4 bolt sculpted al2014 alloycarbon faceplate and titanium hardware csi is a process that permanently bonds carbon to alloy to create a true hybrid product with many of the benefits of aluminum and carbon fsa os99csi ud carbon stem features nb