Three-phase asynchronous motors are widely used in pumps, fans, compressors, conveyors, and machine tools. For engineers and equipment purchasers, choosing the correct motor mounting type is essential because it affects machine structure, compatibility, installation space, maintenance, and overall cost.

According to IEC standards, the three most common mounting types are B3, B5, and B35.
This guide provides a clear and practical explanation of the differences between them and their typical applications.

1. B3 Motors — Foot-Mounted, No Flange, Classical Configuration

B3 is one of the most widely used mounting forms.

Structural Features

• With feet (foot-mounted)

• Without a flange

• Primarily designed for horizontal installation

The motor feet allow easy bolting to a base frame or platform, ensuring stable and reliable operation.

Typical Applications

• Centrifugal pumps

• Industrial fans

• Belt conveyors

• Air compressors

• Machine tools

• Belt-driven equipment

Advantages

• Easy to install and maintain

• Compatible with most traditional machinery

• Cost-effective

In summary:
B3 = Motor with feet, no flange, horizontal mounting.

2. B5 Motors — Large Flange Mounting for Precise Axial Alignment

B5 is structurally different from B3 and is designed for equipment requiring higher concentricity and axial positioning accuracy.

Structural Features

• No feet

• Equipped with a large flange (flange-mounted)

• Typically mounted on a support plate or machine housing

Typical Applications

• Centrifugal pumps

• Mixers and agitators

• Compressors

• Automation equipment

• Gearbox-flange mounting

Advantages

• High concentricity and precise positioning

• Compact installation, saving space

• Suitable for horizontal or vertical mounting

In summary:
B5 = Large flange mounting, compact structure, precise alignment.

3. B35 Motors — Feet + Flange, the Most Versatile Mounting Type

B35 combines the characteristics of both B3 and B5.

Structural Features

• With feet (like B3)

• With a large flange (like B5)

• Supports both foot installation and flange installation

Typical Applications

• Multi-purpose industrial machinery

• OEM equipment

• Pumps and fans

• General mechanical systems requiring flexible installation

Advantages

• Compatible with both B3 and B5

• Highest flexibility and adaptability

• Ideal for manufacturers producing various machine models

In summary:
B35 = Motor with feet + flange, most flexible and universal mounting type.

4. Comparison Table of B3, B5, and B35 Motor Mounting Types

5. How to Choose Between B3, B5, and B35?

• Choose B3 → When using foot mounting on traditional equipment

• Choose B5 → When you need compact installation and precise axial alignment

• Choose B35 → When machine design is flexible, uncertain, or requires dual mounting options

For machine manufacturers and equipment integrators, B35 is often the most versatile choice.

6. Looking for High-Quality Three-Phase Motors?

👉 Highly recommended: www.fuxingmotor.com

Fuxing Motor is a professional manufacturer of three-phase asynchronous motors in China, offering:

• Full mounting options: B3 / B5 / B35

• High-efficiency motors IE2 / IE3 / IE4 / IE5

• OEM customization (special voltage, bearings, frequency inverter motors)

• Exports to 30+ countries including the Middle East, Southeast Asia, and Europe

• Durable, reliable, and suitable for all industrial applications

If you need help selecting the correct mounting type or would like to request a quotation, feel free to ask—I can assist with a complete technical selection guide.