FMSI is the Friction Materials Standards Institute and it acts as the repository for technical data related to brake pads for the industry. It assigns numbers "FMSI Dxxxx" to brake pad outlines to enable brake pad manufacturers to make parts that interchange and fit properly in specific calipers. I was looking around to see if I could find a soft low-dust street pad for the GT350 through the winter, and came across the FMSI numbers for the front and rear calipers. Front GT350/GT350R pad outline: FMSI D1853 Rear GT350/GT350R pad outline: FMSI D1854 (note: FMSI D1718, the C7 Corvette rear pad, also fits this caliper) Where these become useful is when you're looking for brake pads to fit a specific purpose - for instance, if you Google "FMSI D1853", you'll get crosses to Hawk, EBC and Porterfield pad part numbers. It's a useful crosscheck on whether you're looking at parts that'll work or parts that'll almost work. The other time they're really useful is, if you're doing what I was doing and looking for a low-dust ceramic pad to run through the winter, the FMSI numbers cross into most of the major aftermarket brake pad suppliers like Raybestos, Wagner, Power Stop and so on.