V-Belt Cross-Section Identification Chart

What it is

Belt-drive blowers, fans and some compressors use V-belts. The cross section is the size and shape of the belt's trapezoid profile. Two families are common in HVAC:

• Classical sections A, B and C (ARPM IP-20). Industrial-rated belts for larger blowers and multi-belt drives.
• Light-duty / FHP sections 2L, 3L, 4L and 5L (ARPM IP-23). Fractional-horsepower belts for small blowers and single-belt drives.

Cogged versions carry an X (AX, BX). They run cooler and bend around smaller sheaves.

How to identify

• Read the part number on the belt back. The letters are the section and the numbers are the length.
• Classical: for example A36 or BX48. The number is a length code in inches, not the outside length.
• FHP: for example 4L360. The first digit is the top width in eighths of an inch (4/8 = 1/2 in). The number after L is the outside length in tenths of an inch (36.0 in).
• If the print is worn off, measure the top width with a belt gauge or calipers. Measure the length with a belt measuring tape, or use the sheave and center distance.

Section chart

Key points

• 4L and A share a top width, and 5L and B share one too. They are not the same belt. A-section belts are rated for industrial duty; 4L belts are not.
• An A or B belt can often replace a 4L or 5L belt on a single-belt drive. Do not put FHP belts on multi-belt drives.
• A 4L360 and an A34 are close in length. Their numbers differ because the length is measured differently.
• On multi-belt drives, replace all belts as a matched set.

Common mistakes

• Ordering by the length number without knowing which length system it uses.
• Running a worn sheave. A new belt rides low in a worn groove and slips.
• Over-tensioning, which overloads motor and blower bearings. Use the drive maker's tension method.

Governing standards: ARPM IP-20 (classical V-belts); ARPM IP-23 (light-duty FHP V-belts); belt and equipment manufacturer data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.