Gates K040398RB Blue Racing Micro-V Belt Belts are precision ground, not cut, so they fit the pulley with absolute perfection 4 Ribs, .56 inch (14mm) top width, 39.87 inch (1013mm) effective length, 40.375 inch (1027mm) Outside Circumference High-modulus, low-stretch polyester means Herculean strength for high load-carrying capability Aramid reinforcement in a patented EPDM compound for three times the heat resistance and durability of standard belts Patented EPDM compound gives Gates Racing belts extended service life