Understanding V-Belt Markings: What Do They Mean?

If you’ve ever replaced a V-belt on a motor, pump, or industrial machine, you’ve probably noticed a string of numbers and letters printed along the belt. These markings aren’t random—they tell you exactly what type of belt you’re looking at, its size, and sometimes even its construction. Understanding them can save you time, money, and headaches when sourcing replacements.

Let’s break down what these codes mean.

1. Belt Length References (Li, Lw, Ld, Lp, La)

Different manufacturers and standards bodies use slightly different reference points when measuring a V-belt. That’s why you’ll often see designations like Li, Lw, Ld, Lp, or La:

• Li (Inside Length) – Measured along the inner circumference of the belt.

• Lw or Ld (Pitch Length) – Measured along the pitch line (the neutral axis where the tensile cords sit). This is often the most important dimension for power transmission.

• Lp (Pitch Length, alternate) – Sometimes used interchangeably with Lw or Ld depending on the standard.

• La (Outside Length) – Measured around the outer circumference of the belt.

⚡ Tip: Always check the standard (DIN, ISO, RMA, etc.) your equipment uses. A belt marked 13x1000La is not the same as 13x1000Li.

2. Classic and Narrow Wedge Profiles

V-belts come in different cross-sectional profiles. The letters and numbers in their markings often identify this:

• Classical V-Belts (A, B, C, D, E) – The oldest standard, with wider profiles. For example, an A40 is a classic A-section belt with approx. 40″ effective length.

• Narrow Wedge V-Belts (SPZ, SPA, SPB, SPC) – More compact with higher power transmission capability.

• Metric Raw-Edge Narrow (XPA, XPB, XPC) – Cogged or notched for better flexibility and heat dissipation, commonly used in European equipment.

• AVX Belts – A variant of automotive narrow wedge belts, often seen in passenger cars.

3. North American Wedge Standards

In North America, wedge belts are often marked with “V” series codes:

• 3V, 5V, 8V – Denotes belt cross-section and power rating.

  • 3V ≈ SPZ size (9.5 mm top width)

  • 5V ≈ SPB size (15.5 mm top width)

  • 8V ≈ SPC size (25 mm top width)

• 3VX, 5VX, 8VX – The cogged/notched versions, offering better flexibility for smaller pulleys.

4. Special Belt Types

Beyond the standard wedge and classical belts, you might encounter other markings:

• PU (Polyurethane) – Indicates a belt made from polyurethane rather than rubber, common in synchronous/timing belts and some V-belts.

• CX, AX, BX, etc. – Classical cogged versions, e.g., AX for a cogged A-section.

• Double V / Hex Belts (AA, BB, CC) – Designed for serpentine-style drives where the belt contacts pulleys on both sides.

5. Example Marking Breakdown

Let’s decode an example:

“XPB 1600 Lw”

• XPB = Narrow cogged wedge profile, “B” section (≈ 16 mm top width)

• 1600 = Nominal pitch length (in mm)

• Lw = Indicates that 1600 mm refers to pitch length

Another one:
“5VX950”

• 5V = North American wedge profile, 15.5 mm wide

• X = Cogged

• 950 = Effective outside length in tenths of an inch (95.0″)

6. Why This Matters

Knowing how to read belt markings ensures:

• ✅ You order the correct replacement belt.

• ✅ You avoid mismatched lengths (inside vs. outside vs. pitch).

• ✅ You optimize performance and lifespan of your machinery.

Final Thoughts

V-belt markings may look cryptic, but once you know the code, they’re straightforward. Whether you’re working with classical A/B belts, metric SPZ/XPZ types, or North American wedge (3V/5V/8V) standards, these markings are the key to ensuring you get the right belt, every time.