Narrow V-Belts, ideal for transmitting large loads, are commonly designated as 3V, 5V, and 8V. These standardised belts are widely used in North America. With an included angle of 40 degrees, a Narrow V-Belt partially matches the profile of a Wedged V-Belt:

 

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As Narrow V-Belt suppliers in Haryana, India, we agree that it's advisable to use 5V and 3V for SPB and SPZ pulleys, respectively. However, it's not recommended to use SPB and SPZ pulleys on American standard pulleys.