A – The A stands for an “A” section v-belt. This is considered a “Classic” v-belt style that has a top width of ½ (0.5) inches and a thickness of 5/16 (0.312) inches.
21– 21 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 A21 belt is 23 inches (21+2).
Length TypeOutside Circumference
Top Belt Width per strand (inch)0.5
Top Belt Width per strand (mm)13
Nominal Thickness (inch)0.31
Nominal Thickness (mm)8