5L vs B-Section V-Belts: Size Conversion, Notation and Substitution Limits

How to compare 5L and B-section V-belts in a catalog: length basis, notation and the checks needed before any substitution is proposed.

5L and B-section belts are named in different systems, so their part numbers cannot be compared digit for digit. Record the section, the length value and the length basis separately, take any conversion from the manufacturer’s published table, and label the result a candidate that still needs engineering review.

What to compare

Item	5L	B section	Status
Top width and thickness	Needs review	Needs review	Take from manufacturer catalog
Length basis behind the number	Needs review	Needs review	Take from manufacturer catalog
Typical duty (light vs industrial)	Needs review	Needs review	Take from IP-20 or manufacturer
Conversion between numbers	Only via a published table	Only via a published table	No formula is given here

Worked example (illustrative, no real part numbers)

A supplier file lists 5L-EXAMPLE with no length basis, and your catalog holds B-EXAMPLE. The right output is not a merge. Record each as its own SKU, leave the basis blank until the catalog page is found, and open a candidate link only once a manufacturer table supports it.

Substitution limits

A size correspondence is not engineering approval. Check the length type (pitch, datum, effective or outside), section, construction (wrapped, raw-edge, cogged), band count, matched sets, sheave groove, power rating, temperature, oil and static conductivity, and brand notation. Never promise automatic substitution. See the V-belt attribute template and how to read V-belt part numbers.

Sources

No external source has been verified yet. To consult: Gates and Carlisle V-belt catalogs, Dayco and Optibelt technical pages, RMA/MPTA/ARPM IP-20.

Attribute Library

V-Belt Attributes & Template

Fields for section, length basis and construction.

Guide

How to Read V-Belt Part Numbers

Parsing model for belt designations.

Playbook

Find Functional Equivalents

Attribute-based comparison workflow.

Guide

Product Relationship Types

Labelling candidates without over-claiming.

FAQ

Can I convert a 5L belt number to a B-section number by formula?

Not without a sourced rule. The two systems can use different length bases, so a number should only be converted using the manufacturer’s published table, and the result should be stored as a candidate, not an approved substitute.

Is a 5L belt the same as a B-section belt?

This page does not claim so. Any relationship must be confirmed in manufacturer documentation, and even then it is a naming and size correspondence, not an engineering approval.