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How to Read a V-Belt Size

by Kelvin Hayes

An automotive V-belt, also referred to as a pulley, can either transfer power from one engine element to another or change the speed and torque of engine components. The latter is done by installing a belt with a different pitch angle. All V-belt numbers start with either a 4L or 3L, which indicate 12.5mm or 9.5mm belt widths. After every prefix is a three-digit number that indicates the V-belt's length in inches.

Step 1

Read the outside surface of the belt for the prefix 4L or 3L.

Step 2

Read the three-digit number after the prefix to identify the belt's length. For example, if the belt reads 4L460, you know the belt is 12.5mm wide, with a 46-inch outside circumference.

Subtract 2 inches for 4L belts or 1 1/2 inches for 3L belts to determine the inside circumference of the belt. Using the same example, the 4L460 V-belt has an inside circumference of 44 inches.

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