V-belts (inch A / B series) | A29–A53, B38–B56
11 classical inch V-belt sizes — A series 4 sizes (A29 / A33 / A39 / A53) + B series 7 sizes (B38 / B40 / B41 / B44 / B54 / B55 / B56). Heavy-duty rubber construction for drives on CNC machines, air compressors, water pump motors, textile machines and conveyor lines.
The V-belt is one of the main power transmission elements in industrial machinery, transmitting power by friction from the wedging of its V-shaped section in the pulley groove. Inch sizes are marked “letter + number”: the letters A, B, C, D, E indicate the section (A = 13 mm × 8 mm, B = 17 mm × 11 mm) and the number is the inside length in inches — a standard classification used throughout the machinery industry.
All 11 belts in this series are heavy-duty wrapped construction: a fabric cover on top resists wear, high-strength tensile cords in the middle carry the load, and the V-shaped rubber base wedges into the pulley groove. We supply power transmission consumables and spare parts for semiconductor fabs and general machinery MRO customers, with complete A–E sections and inch / metric lengths available.
Specifications (by size prefix)
| Series | Section (W × H) | Angle | Part numbers in this series | Inside length range | Typical power |
|---|---|---|---|---|---|
| A series (inch, 4 sizes) | 13 mm × 8 mm | 40° | A29, A33, A39, A53 | 29–53 in. (approx. 737–1346 mm) | 0.4–5 kW |
| B series (inch, 7 sizes) | 17 mm × 11 mm | 40° | B38, B40, B41, B44, B54, B55, B56 | 38–56 in. (approx. 965–1422 mm) | 1.5–15 kW |
Note: section dimensions and angle follow the general standard for classical inch V-belts (ISO 4184 / ANSI/RMA IP-20). Typical power is a reference value for continuous drive with a single belt; actual values depend on speed, pulley diameter and operating hours (typical; depends on application). Power adds up with multiple belts in parallel.
Applications
V-belts are used in large quantities as drive parts in electronics manufacturing and general machinery — from air compressor systems in SMT plants, facility pumps and CNC machining centers to conveyor motors. Four typical applications and common spare part needs:
- CNC machine / machine tool spindle drives. The drive between spindle and motor often uses B series V-belts (higher power capacity), commonly B41–B56, with two or more belts in parallel for 5–15 kW spindle power. Aged belts cause unstable spindle speed and dimensional deviation; include them in annual maintenance replacement. Typical: B44 / B54 / B56
- Air compressor / vacuum pump drives. Oil-free or screw air compressors often use two or three B series belts in parallel (5.5–22 kW class). Compressors start and stop frequently and run for long hours; heavy-duty belts extend the replacement interval. SMT facility and semiconductor fab vacuum systems commonly use B38–B55. Typical: B38 / B41 / B55
- Textile machines / food packaging lines. Multi-axis drive trains on textile machines and automatic food packaging machines mix A and B series: B series for the main drive, A series for branch drives. Packaging machines have short cycle times and belts see repeated tension changes; a tension check every 12–18 months is recommended (typical; depends on application). Typical: A33 / A39 / B44
- Facility water pump motors / fans. Facility water treatment, cooling tower fans and circulation pumps mostly use A series (0.75–3.7 kW class). Fans and pumps run continuously for long periods; keep spares listed to avoid unexpected downtime. Common range A29–A53. Typical: A29 / A33 / A53
Selection: recommended section and length by equipment type
| Equipment type | Power range | Recommended section | Part numbers in this series |
|---|---|---|---|
| Small fans, water pump motors, appliance motors | 0.4–2.2 kW | A series | A29, A33, A39 |
| Light machine tools, conveyor motors | 2.2–5 kW | A series (multiple belts) or B series (single belt) | A53 / B38, B40, B41 |
| Air compressors, CNC spindles, textile machines | 5–15 kW | B series (two or three belts in parallel) | B44, B54, B55, B56 |
| Large air compressors, large fans | 15–37 kW | C series (22 mm × 14 mm, not in this series) | Quote on request |
Note: power ranges are reference values for continuous drive with a single belt; power adds up with multiple belts. Actual selection must consider speed, pulley diameter, operating hours, ambient temperature and start / stop frequency (typical; depends on application). For multi-belt drives, buy the whole set from the same batch so tension is even.
Inch vs. metric SP series, standard vs. heavy-duty: three key differences
There are two main V-belt standards: inch classical (ANSI/RMA IP-20, ISO 4184 classical) and metric narrow V-belts (DIN 7753, ISO 4184 narrow). Their size code systems are completely different and cannot be mixed.
Why is the number in inches and not mm? Inch V-belts originated in the USA, and the number is the inside length in inches. Conversion: A29 = 29 in. inside length × 25.4 = approx. 737 mm; B56 = 56 × 25.4 = approx. 1422 mm. The actual outside length (measured around the outside of the belt) is slightly longer than the inside length because the section has thickness. When ordering, use the size code directly; converting to mm with tables makes errors more likely.
With the wrong size code system, the belt will not fit the pulley at all. With the wrong construction grade, belt life can be much shorter. Three key differences to clarify first:
| Item | Inch classical (this series) | Metric narrow V-belt SP series | Key difference |
|---|---|---|---|
| Size code | A29 / B56, etc. | SPA1250 / SPB1400, etc. | Letter + inches vs. letter + metric length in mm |
| Section (A vs. SPA) | 13 × 8 mm | 13 × 10 mm (narrow, taller) | SP sections are narrower and taller; one belt transmits more power, allowing narrower pulleys for the same power |
| Angle | 40° (standard) | 40° (standard) | Same |
| Typical applications | Conventional machinery, agricultural machinery, facilities | Limited space, high-power drives | Not interchangeable; the pulley groove decides |
Note: this page covers inch A / B series; metric SP series and other sizes are available on request.
When must you choose heavy-duty? Four situations: (1) frequent start / stop (automatic packaging machines, forklifts, conveyor starters); (2) high starting shock (air compressors, crushers, meat grinders); (3) high speed (CNC spindles ≥ 3000 rpm, high-speed fans); (4) long continuous operation (24-hour process equipment, cooling tower fans). Standard belts are enough for light loads, low speeds and intermittent operation (all belts on this page are heavy-duty; standard belts available on request).
Selection process and 5 common failure signs
In practice, selection does not start from the belt size but works back from the equipment. The full process:
Check the equipment nameplate (drive power kW, motor speed rpm) → measure the pulley groove (A / B groove, single / multiple grooves) → measure the center distance between the pulleys (to work out the required inside length) → assess operating conditions (start / stop frequency, continuous hours) → choose the construction grade (standard or heavy-duty).
5 common failure signs (replace when you see them):
- Cracks or brittleness on the belt sides — rubber aging, heat or UV degradation
- V-shaped contact surface on the bottom worn flat or through to the cords — lower efficiency, slipping
- Squealing or slapping noise during operation — insufficient tension, uneven wear in multi-belt sets
- Belt stretched so far it can no longer be tensioned (tension adjustment screw at its limit)
- Shiny, deformed belt sides — excessive friction with the groove, worn pulley groove
Rule for multi-belt drives: replace the whole set from the same batch. Two- or three-belt drives (common on air compressors, CNC spindles and textile machines) are designed so each belt carries an equal share of the load. Mixing new and old belts overloads the new belt so it breaks early, while the old belt slips and ages faster. Buy the whole set from the same batch (same lot number) so length tolerances match. When replacing, also check pulley groove wear; if the wear depth is ≥ 1 mm, replacing the pulley as well is recommended.
Tension installation (simple method): press the belt at the midpoint between the pulleys; deflection should be about 1/64 of the span (typical; depends on application), or measure with a tension meter to the manufacturer’s specified value. Too tight shortens bearing life and increases power consumption; too loose causes slipping, heat and insufficient torque. Check tension again after 24–48 hours of operation with a new belt, because new belts stretch initially.
Standard reference
ISO 4184 “Belt drives – Classical and narrow V-belts – Lengths in datum system” | Issued by: International Organization for Standardization (ISO). Refer to the current edition published by the issuing body.
Email us for a quote: [email protected]