An “A” style belt are typically industrial belts that are measured for size on the inside of the belt whereas “L” style belts are measured on the outside.
The size difference between an ” A ” belt and a ” L ” belt is always 2 inches.
Therefore, if you have an “A-40″ belt and you wish to replace it with a ” L ” belt you will need a “4L420″ to replace it.
Similarily “B” style belts are measured for size on the inside of the belt as well – however there is difference of 3 inches to a ” L ” belt
So, if you have a B-56 belt that you want to replace with a ” L ” belt you will need a 5L590 belt to fit properly.
Kevlar V belts are traditionally used with outdoor power equipment, these are coded as 4L,5L The Kevlar is critical when drives need reverse bending such as on idlers.