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 durability and value Fibratek: Selle Italia's latest cover material offering supreme durability and comfort 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)