Hello, each letter corresponds to a different feature of the implant which I will explain below: S - the first letter can be "S" or "T". This refers to whether the implant has a "Smooth" or "Textured" surface. S - the second letter refers to the gel thickness within the implant. It can be can be "R" for "Responsive", which is a very deformable implant, "S" for "Soft Touch", which is a thicker gel that holds its shape more, or "Cohesive", which is an even thicker, firmer gel. F - the last letter(s) refer the shape or profile of the implant. "L" means "Low Profile", "LP" means "Low Plus Profile", "M" means "Moderate Profile", "F" means "Full Profile", and "X" means "eXtra Full Profile" Therefore the two implants you are comparing are both smooth surfaced, full profile implants. However, one has Soft Touch gel fill and one has thicker Cohesive gel fill. It is important to note that in Canada, for reasons that are unclear to me, the company markets the Soft Touch implants as "Truform II" and the Cohesive implants as "Truform III", but they are the same devices.