What size is a B belt?

A B-section V-belt measures 21/32 inch (16.7mm) across the top width and 13/32 inch (10.3mm) in height. The belt angle is 40 degrees. B belts range from 21 inches to over 300 inches in inside circumference length.

What is the difference between B and 5L belts?

B and 5L belts share the same 21/32 inch top width but differ in height: B belts are 13/32 inch tall while 5L belts are 3/8 inch tall. This means B belts ride slightly deeper in the pulley groove. B belts use inside circumference measurement while 5L belts use outside circumference. They are close but not always a direct interchange due to the height difference.

How are B belts measured?

B belts are measured by inside circumference. Wrap a tape measure around the inside surface of the belt (the side that contacts the pulley groove) and measure the total length in inches. That measurement is the B belt number. For example, a belt measuring 68 inches on the inside is a B68.

What are B belts used for?

B-section V-belts are used in heavy-duty industrial applications including large HVAC systems, industrial pumps, air compressors, agricultural machinery, manufacturing equipment, conveyor systems, and mining or aggregate processing. They handle higher horsepower loads than A-section belts.

Can I use a 5L belt instead of a B belt?

Not always. While B and 5L belts share the same 21/32 inch top width, B belts are slightly taller (13/32 inch vs 3/8 inch). This means a B belt rides deeper in the pulley groove. In many applications a 5L belt will work as a replacement, but check your pulley groove depth. If the groove is designed for a B belt, a 5L may ride too high and slip under heavy loads.

B Belt Guide - B Section V-Belt Sizes, Dimensions & Cross Reference

The B-section is an industrial-grade V-belt measuring 21/32" wide x 13/32" tall. B belts are among the most common industrial V-belts, used in heavy-duty power transmission applications ranging from large HVAC systems to manufacturing equipment. Their robust construction handles higher horsepower loads than A-section belts.

B Belt Specifications

Specification	Value
Top Width	21/32" (16.7mm)
Height	13/32" (10.3mm)
Belt Angle	40°
Minimum Pulley Diameter	4.6" (5.4" recommended)
Length Range	21" to 300"+ (inside circumference)
Construction	Industrial rubber with polyester cord

Understanding B Belt Part Numbers

B68 = B-section belt, 68" inside length. B belts are measured by INSIDE circumference, just like other industrial-grade classical V-belts. The number after the "B" prefix is the belt's inside length in inches.

B vs 5L Belts: Side-by-Side Comparison

Feature	B Belt	5L Belt
Top Width	21/32"	21/32"
Height	13/32"	3/8"
Measurement Method	Inside length	Outside length
Part Number Example	B68 = 68" inside	5L710 = 71" outside
Grade	Industrial	Fractional Horsepower (FHP)
Key Difference	B is slightly taller (13/32" vs 3/8") — rides deeper in the pulley groove. Not always a direct swap.

Common Applications for B Belts

B-section V-belts handle heavier loads than A belts and are found in demanding industrial environments, including:

Heavy industrial drives — high-horsepower motor applications
Large HVAC systems — commercial air handlers, cooling towers, and roof-top units
Pumps — industrial water, chemical, and process pumps
Air compressors — large reciprocating and rotary screw units
Agricultural machinery — combines, tractors, balers, and grain handling
Manufacturing equipment — stamping presses, mixers, and heavy-duty conveyors
Conveyor systems — medium to heavy-duty material handling and processing lines
Mining and aggregate — crushers, screens, and processing equipment

How to Measure a B Belt

B belts are measured by inside circumference. Lay the belt flat and measure around the inside surface (the side that contacts the pulley groove). The total length in inches gives you the B belt number. For example, if the inside measures 68 inches, you need a B68.

For worn or broken belts, measure center-to-center between the pulleys and use a belt length formula, or visit our complete V-belt measurement guide for detailed instructions.

Shop B Belts at EVbelts.com

We carry a complete selection of B-section V-belts from B21 through B300 with fast shipping.

Popular sizes: B33, B48, B68, B75, B90, B128

Browse All B Belts →

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