This set includes two belts, one BX series cogged drive belt, and one BX series cogged follower belt, which are designed for use on the bandwheels of the HM126/HM130 & HM130MAX portable sawmill. The drive belt runs from the engine clutch to the bandwheel, while the follower belt runs on the opposing bandwheel. It is recommended that the belts are replaced when they are within 1/16 inch (1.6mm) of the top surface of the belt to the edge of the bandwheel. For sawmills manufactured in 2015 and later, the recommended belt sizes are BX79 and B57, while for sawmills manufactured in 2014 and earlier, the recommended belt sizes are BX77 and B57.