FSA SL-K Stem. The FSA SLK Stem is as light as it is strong, and it's plenty strong. FSA's SL-K Carbon Stem is constructed from a mix of CNC machined 2014 aluminum and a carbon fiber composite. To guarantee rigidity, FSA 3D forged the aluminum stem body. The benefits to you are a heightened stiffness, with weight comparable to carbon fiber, at a considerably lower cost. To maintain the flow of weight savings, the SL-K uses a carbon fiber face plate with chromoly hardware.