Important reminder: the length of rubber V-belt O A B C D E is the inner circumference, measured in inches. the length of SPZ SPA SPB SPC is the pitch length, measured in millimeters. the length of rubber V-belt 3V 5V 8V is the pitch length, measured in inches. for example, the pitch length of SPB1600 is 1600mm, the pitch length of 5V1600 is 160 inches (equivalent to the international standard pitch length of 4064mm), while the inner circumference of B63 is 63 inches (equivalent to the international standard inner circumference of 1600mm, so some countries label B63 as B1600)