V-Belt Size Chart: Cross-Section Reference & Identification Guide

What Is a V-Belt?

A V-belt is a loop of flexible material — typically rubber-reinforced with polyester or aramid cord — used to transmit power between rotating shafts via sheaves (pulleys). The trapezoidal cross-section wedges into matching grooves in the sheave, creating friction-driven power transfer without the noise, lubrication demands, or complexity of chain drives.

V-belts are used across industrial machinery, agricultural equipment, HVAC systems, compressors, pumps, lathes, and workshop tools. When a belt fails, knowing the correct replacement size is critical: the wrong section or length causes slipping, premature wear, bearing overload, or complete drive failure.

This guide covers every V-belt cross-section in Australian use, how to decode belt part numbers, how to measure a belt when the number is missing, and how to select the right belt type for your application.

V-Belt Cross-Section Reference Guide

V-belts are classified first by their cross-section — the shape and size of the belt's profile when viewed from the end. The cross-section determines which sheave grooves the belt fits and how much power it can transmit. Two main families are in common Australian use: classical (wrapped) belts and narrow/wedge belts.

Classical V-Belt Cross-Sections

Classical V-belts use a 40° included angle and are designated by a letter (Z, A, B, C, D, E) in ascending width. They remain the most common type in general industrial and agricultural applications.

Note: The number in brackets (e.g., Z = 10, A = 13) refers to the ISO/metric top width in millimetres. You may see belts marked as "13A" or "A13" interchangeably — both refer to the A section. Classical belt sections were originally defined in imperial inches (per ANSI/RMA IP-22); the ISO metric figures are standardised equivalents and differ slightly from exact inch conversions — so a Z belt measuring 9.5mm is correct, not undersized.

Narrow (Wedge) V-Belt Cross-Sections — SP Series

Narrow V-belts use a steeper 34° included angle and a taller, narrower profile than classical belts. This geometry allows them to transmit significantly more power in a smaller sheave groove. Narrow belts are specified where drive space is limited or where classical belts would require multiple strands.

Important: Classical and narrow belts with the same top width are not interchangeable. The different angles (40° vs 34°) mean they will not seat correctly in each other's sheave grooves. Always confirm the sheave type before ordering.

Fractional Horsepower (FHP) Belts — 3L, 4L, 5L

FHP belts are found in smaller appliances, domestic tools, and light equipment. They use a narrower 40° profile and are designated 3L, 4L, or 5L.

How to Read a V-Belt Part Number

If the belt has a readable marking, the part number tells you everything you need. The format varies slightly between classical and narrow belts.

Classical Belt Designation

Classical V-belt numbers follow the pattern: [Section Letter] + [Length Number]

The length number represents the belt's datum (pitch) circumference — measured at the neutral axis of the belt, not the outside or inside edge. In imperial-designated belts (most common in Australia), the number is in inches. In metric-designated belts, the number is in millimetres.

Some manufacturers include a prefix (e.g., "HB68" for a heavy-duty B68, or "XB68" for a cogged B68). The core section and length identification remains the same.

Narrow Belt Designation

Narrow (SP series) belts follow: [SP Section] + [Datum Length in mm]

Narrow belts are always metric-designated — the number is always in millimetres.

Outside Circumference vs Datum Length

The datum (pitch) circumference is not the same as the outside circumference of the belt. When measuring a belt manually, you are usually measuring the outside circumference. The relationship between outside circumference (OC) and datum circumference varies by section:

Example: You measure an old A section belt and get an outside circumference of 1042mm. Subtract 25mm → datum circumference = 1017mm ≈ 1016mm → the belt is an A40 (40" × 25.4 = 1016mm).

V-Belt Size Chart — Classical Belts (Common Australian Sizes)

The tables below list the most common classical V-belt sizes stocked in Australian industrial supply. Belt length availability extends beyond this range — consult a catalogue for full listings. All lengths are datum circumference.

A Section — 13mm Top Width

B Section — 17mm Top Width

C Section — 22mm Top Width

D Section — 32mm Top Width

Z Section — 10mm Top Width

V-Belt Size Chart — Narrow (SP Series) Common Sizes

SPZ Section — 10mm Top Width

SPA Section — 13mm Top Width

SPB Section — 17mm Top Width

SPC Section — 22mm Top Width

How to Measure a V-Belt When the Number Is Missing

When the belt markings are worn or missing, you can identify the replacement in three steps.

Step 1 — Identify the Cross-Section

Remove the belt from the machine or lay it flat. Measure the top width (widest face) and height (thickness, measured through the centre of the belt from top face to bottom). Match your measurements against the cross-section table at the top of this guide.

A simple go/no-go check: place the belt across a flat surface and hold a ruler across the top. The width is your primary identifier. If a belt measures 17mm wide and 11mm high, it is a B section classical belt.

Step 2 — Measure the Length

There are two practical methods:

Method A — Belt on the machine: Wrap a piece of string around the belt path, following the exact route the belt takes around both sheaves. Mark where the string meets itself, lay it out straight, and measure. This gives you the datum circumference directly (close enough to select a belt). Add or subtract centre distance adjustment when reinstalling.

Method B — Belt in hand: Wrap a flexible tape measure or string around the outside of the belt loop and measure the full outside circumference. Then apply the OC-to-datum conversion from the table above to arrive at the datum length.

Step 3 — Cross-Reference to Part Number

With section and datum length identified, match to the size charts in this guide. If your measured datum falls between two standard sizes, always select the shorter belt — most drives allow a small amount of adjustment at the motor mounting, and a slightly short belt is better tensioned than one that is too long and cannot be properly tensioned.

V-Belt Types: Which One to Choose

Classical Wrapped V-Belts

The classical wrapped V-belt was invented in 1917 by John Gates of the Gates Rubber Company — the same Gates who remain the world's largest V-belt manufacturer today. Browse Gates V-belts at AIMS Industrial. The standard choice for the majority of industrial and agricultural drives. The outer fabric wrap (usually polyester or cotton/polyester blend) protects the belt from oil, heat, and abrasion. Well-suited to drives with multiple belt strands, reversing loads, and applications where belts are replaced individually.

Cogged (Raw Edge) V-Belts

Cogged belts have moulded notches (cogs) on the inner surface, which increase flexibility and reduce heat buildup in tight-radius applications. They can transmit more power than a classical wrapped belt of the same cross-section and run cooler on small-diameter sheaves. Identified by an "X" prefix or "HC" suffix (e.g., XB68, B68HC).

Use cogged belts when: sheave diameter is close to the minimum for that section; drive runs hot; efficiency is a priority.

Narrow Wedge V-Belts (SP Series)

Up to three times the power capacity of an equivalent classical belt due to the deeper wedging action. Used where space is limited or where a classical drive would require four or more belt strands. Require SP-specific sheave grooves — cannot be used with classical sheaves.

Banded / Joined V-Belts

Multiple belts joined laterally by a top band, creating a single unit. Used on drives subject to vibration, pulsating loads, or vertical shaft arrangements where individual belts would roll or whip. Common on agricultural equipment (headers, grain augers) and reciprocating compressors. Identified by a number prefix indicating belt count (e.g., 3B68 = three B68 belts joined).

Variable Speed V-Belts

Wide-section belts used in variable pitch sheave drives. Not covered by standard section designations — always specify by machine OEM part number for these applications. For full coverage of industrial Multi-Speed belts (Gates W-section and HV), powersports CVT belts (UTV, ATV, snowmobile), and small-vehicle CVT (go-karts, dune buggies, scooters), see our Variable Speed Belt Guide.

V-Belt Installation and Tensioning

Never Force a Belt Over a Sheave

Always slacken the drive (move the motor or take-up bearing toward the driven shaft) before fitting a new belt. Forcing a belt over a sheave flange damages the cord reinforcement, shortening belt life dramatically. Even if a belt appears to go on without damage, internal cord breakage may not be visible.

Sheave Alignment

Before tensioning, check that sheaves are correctly aligned in both planes — angular misalignment (sheaves not parallel) and parallel misalignment (sheave faces offset). Use a straight edge or laser alignment tool across the sheave faces. Misalignment causes uneven wear on one side of the belt, rapid cord fatigue, and bearing overload.

Correct Belt Tension

Over-tensioning is the most common cause of premature V-belt and bearing failure. Under-tensioning causes slipping, heat, and rapid wear. The standard field check is the deflection method:

1. Measure the span length (the straight distance between the two sheave contact points on the slack side).
2. Apply a perpendicular force at the midpoint of the span.
3. Correct deflection is approximately 16mm per 1000mm of span (or 1/64" per inch of span).
4. The force required to achieve this deflection should match the belt manufacturer's specification for the section and speed — typically 2–6 kg (20–60N) depending on section size.

New belts should be tensioned slightly above the target, run for 30 minutes under load, then re-tensioned — they will seat and relax slightly during run-in.

Sheave Groove Condition

Inspect sheave grooves for wear before fitting new belts. A worn groove becomes rounded and loses its wedging action, causing the new belt to bottom out in the groove rather than ride on the flanks. A belt that bottoms out will slip immediately regardless of tension. If the groove is worn, replace the sheave before fitting new belts.

Mixed Belt Sets

When running multiple belts in a multi-groove drive, always replace all belts as a matched set. Mixing old and new belts results in uneven load sharing — the shorter, stiffer old belts carry more load and fail prematurely, taking the new belts with them shortly after.

Common V-Belt Failure Modes and Causes

Minimum Sheave Diameter by Belt Section

Running a V-belt on a sheave smaller than the recommended minimum diameter causes excessive bending stress on the tension cord, dramatically shortening belt life. The following are recommended minimum pitch diameters.

For the full pulley-side reference — including the SPZ/SPA/SPB/SPC profile detail, taper lock vs pilot bore mounting, alignment with Gates laser tools, and the 1/3 wear rule with the Gates pulley gauge set — see our Pulley Types Guide.

Storage and Handling

V-belts are sensitive to ozone, UV, heat, and deformation. Store belts in a cool, dry location away from direct sunlight and fluorescent lighting (which emits ozone). Do not hang belts on nails or hooks that force them into sharp bends — store coiled loosely or flat. Belts stored correctly in original packaging have a shelf life of several years; belts that have been kinked, oil-contaminated, or heat-exposed should be replaced regardless of apparent condition.

When removing a belt from service for inspection or temporary storage, mark it with the machine and position before removal. Reusing a belt in the exact same installation position (same running direction) reduces run-in wear.

Frequently Asked Questions

What does the number in a V-belt part number mean?
In a classical V-belt designation (e.g., B68), the letter indicates the cross-section and the number indicates the datum (pitch) circumference. For imperial designations common in Australia, the number is in inches — B68 has a 68-inch datum circumference (1727mm). For narrow SP series belts (e.g., SPB1600), the number is always in millimetres — SPB1600 has a 1600mm datum circumference.

What is the difference between datum length, inside circumference, and outside circumference?
Datum (pitch) length is measured at the neutral axis of the belt — the theoretical line within the belt where the cord reinforcement sits, and where the belt neither stretches nor compresses during bending. Inside circumference is shorter (measured at the inner surface) and outside circumference is longer (measured at the outer surface). V-belt part numbers reference datum length, not inside or outside circumference. When measuring a belt manually, you typically measure outside circumference and subtract the correction factor for your section to obtain the datum length.

Can I replace a classical V-belt with a narrow (SP) belt?
Not directly, without also replacing the sheave. Classical and narrow belts use different groove profiles — 40° for classical, 34° for narrow SP. Fitting a narrow belt to a classical sheave (or vice versa) will cause the belt to sit incorrectly in the groove, resulting in rapid wear, reduced power transmission, and premature failure. If you are upgrading from classical to narrow belts for higher power capacity, both the belts and sheaves must be changed together.

How do I know if my V-belt sheave groove is worn out?
Hold a new belt of the correct section against the groove. The belt should contact the groove flanks and sit proud of the groove top — not bottom out. If the belt sinks to the bottom of the groove and contacts the groove base, the groove is worn to the point where it can no longer wedge the belt effectively. A new belt will slip immediately. Replace the sheave before fitting new belts. Also check for groove roughness or scoring, which causes rapid belt wear.

How many V-belts should I run on a multi-groove drive?
The number of belts in a multi-groove drive is determined by the power to be transmitted, the belt section, and the drive design. Always replace all belts in a multi-belt drive as a complete matched set — never add a single new belt to a set of used belts. Old and new belts of nominally the same size have different effective lengths due to stretch; mismatched sets cause uneven load sharing, premature failure of all belts, and accelerated sheave wear.

What is the difference between a cogged V-belt and a standard V-belt?
A cogged (notched or raw edge) V-belt has moulded transverse notches on its inner face. These notches allow the belt to bend more easily around small-diameter sheaves, reducing heat buildup and improving efficiency. Cogged belts are the same cross-section as classical belts and fit the same sheave grooves — they are a direct drop-in replacement for classical wrapped belts with improved performance. They are particularly beneficial where sheave diameters are close to the minimum for the section, and in high-speed, high-temperature applications.

Why do V-belts squeal?
Belt squeal almost always indicates slipping — the belt is not transmitting the required torque and is sliding against the sheave groove. Common causes are: insufficient tension, worn sheave grooves that can no longer wedge the belt, oil contamination on the belt or sheave faces, or a belt that is the wrong section for the sheave groove. Applying belt dressing is a temporary fix that does not address the root cause — check tension first, then inspect sheave condition, then check for oil contamination.

Can a V-belt run in both directions?
Standard single-strand V-belts can run in either direction — they are symmetric in the rotation direction. However, if a belt has been run in one direction, the cord reinforcement takes on a slight set; re-using in the same direction produces less stress. Banded belts and some agricultural belts are marked with a preferred running direction and should be reinstalled accordingly. Variable-speed belts and some cogged belts may also have a preferred direction — check the manufacturer's marking.

What is a banded V-belt and when should I use one?
A banded (joined) V-belt consists of two or more individual V-belts joined laterally by a reinforced top tie band, forming a single rigid unit. Banded belts are used on drives subject to vibration, shock loads, pulsating input (e.g., reciprocating compressors, harvesting equipment), or drives with long spans where individual belts would whip and roll out of the groove. They must be used with sheaves specifically grooved for banded belts, which have a relieved channel between grooves to accommodate the tie band.

How long should a V-belt last?
Under correct conditions — proper tension, aligned sheaves, correct belt type, no contamination, appropriate sheave diameter — a quality V-belt will typically last 20,000–25,000 hours of operation. In practice, most industrial belts are replaced on condition or at scheduled maintenance intervals well before that. Belts on agricultural equipment running seasonally may last several seasons if stored correctly. The most common causes of premature failure are misalignment, incorrect tension, sheave wear, and oil contamination — all of which are preventable with correct installation and maintenance.

What causes V-belt slippage?
V-belt slippage — where the belt slides against the sheave face instead of transmitting full torque — has four main causes. (1) Insufficient tension: the most common cause; the belt cannot generate enough friction to transmit the required load. Retension to the manufacturer's specified deflection force. (2) Misalignment: angular or parallel misalignment forces the belt to work across the groove rather than straight through it, reducing effective contact and grip. (3) Worn or glazed sheave grooves: a groove that has worn smooth or bottomed out can no longer wedge the belt; the belt sits on the groove base rather than the flanks and loses its wedging action entirely. (4) Contamination: oil, grease, or water on the belt or sheave surface dramatically reduces friction. Contamination-affected belts cannot be restored by cleaning — replace the belt and address the source of contamination.

Can V-belts stretch?
V-belt cord reinforcement — polyester or aramid — does not stretch significantly in normal service. However, all new V-belts undergo a run-in period during which the cord beds into the belt carcass and the belt takes on a slight set to the sheave curve. This run-in elongation typically occurs in the first 24–48 hours of operation and results in a measurable reduction in effective tension. For this reason, all V-belts should be retensioned after the first day of operation. Failure to retension after run-in is one of the most common causes of premature belt slip, squealing, and reduced service life — particularly on higher-load drives where initial tension is critical.

Are rubber or polyurethane V-belts more durable?
Classical rubber V-belts — reinforced with polyester or aramid cord — remain the standard for most industrial and agricultural applications. They tolerate a wide temperature range, flex well around smaller sheaves, and are available in every standard section and length. Polyurethane V-belts offer superior abrasion resistance and better resistance to oil contamination, and are dimensionally more stable than rubber. However, polyurethane belts are stiffer, perform less well at low temperatures, and require sheave diameters within tighter minimums — they can crack prematurely on drives with undersized sheaves. For standard industrial drives, rubber belts are the correct default choice. Polyurethane suits applications with high oil exposure or abrasive environments where the drive geometry is appropriate.

For your V-belt replacement needs, browse AIMS Industrial's full range of V-belts — classical, narrow wedge, cogged, and banded belts stocked for fast Australia-wide dispatch.