A?? The A stands for an ?A? section v-belt.?This is considered a ?Classic? v-belt style that has a top width of ? (0.5) inches and a thickness of 5/16 (0.312) inches.
78? 78 inches is the inside circumference of the belt.?For A-section v-belts, the outside circumference is found by adding 2 inches to the inside length of the belt.?So, the outside circumference of the A78 belt is 80 inches (78+2).