Classic Flat shape that has always distinguished the Flite family, combined with the more compact design of the Boost geometry TI 316: 7mm rails are hollow titanium, a balance of strength and light weight Manganese: 7mm rails made of a Manganese and CrMo alloy for excellent durabilty and value Fibratek: Selle Italia's latest cover material offering supreme durability and comfort SoftTek: Polyurethane cover for high levels of comfort and durability For more information on idmatch visit http://www.selleitalia.com/en/idmatchsystem/ L3: “Wide” intertrochanteric distance and high pelvic rotation (Flow and SuperFlow saddles) S3: “Narrow” intertrochanteric distance and high pelvic rotation (Flow and SuperFlow saddles)