What is the difference between foot-mounted and flange-mounted gearboxes?

Foot-mounted (IEC B3): Four legs on the bottom of the housing; bolted to a flat foundation (floor, frame, or bedplate). Advantages: low cost, flexible positioning, easy to access for maintenance. Disadvantages: legs transmit vibration to foundation; misalignment risk if foundation is not perfectly level. Flange-mounted (IEC B5 or B14): Mounting flange on one face (B5) or two faces (B14) of the housing; bolted directly to motor or driven equipment. Advantages: compact, high rigidity, eliminates misalignment risk (motor and gearbox are co-axially aligned). Disadvantages: higher cost, less accessible, less flexible installation.

What is a torque arm and when is it used?

A torque arm is a rigid bracket attached to the gearbox that reacts output torque forces to the foundation (or frame), preventing the gearbox from rotating due to reaction torque. Essential for shaft-mounted gearboxes and loose foot-mounted installations where output torque is high. Without a torque arm, the gearbox would rotate slightly around the motor axis (torsional twisting), straining output shaft bearings and causing vibration. Torque arms are standard for industrial hoist gearboxes, mixer drives, and any application where output torque exceeds 500 N-m or misalignment must be prevented.

What is shaft-mounted gearbox and what are its advantages?

Shaft-mounted gearbox bolts directly onto the load shaft (e.g., rotating drum, pulley) without an intermediate coupling. The gearbox input accepts the motor coupling, and the output flange is integrated into the load assembly. Advantages: (1) Eliminates one coupling, reducing cost and maintenance; (2) Compact, occupying less space; (3) Improved alignment (gearbox is directly on the load); (4) Reduced inertia and vibration (fewer connections). Disadvantages: (1) Entire gearbox weight hangs on the load shaft, requiring robust shaft design; (2) Load shaft must be supported by adequate bearings to handle gearbox radial and axial loads; (3) Less flexible—gearbox cannot be easily moved or swapped; (4) Requires mounting-specific designs from the gearbox manufacturer. Used mainly in heavy-duty applications like conveyor drives and materials handling.

What do IEC codes B3, B5, B14 mean?

IEC 60034-7 defines standard mounting codes for electric motors and gearboxes: (1) B3 (Foot-mounted): Four feet, vertical arrangement, motor shaft horizontal; (2) B5 (Flange-mounted, one face): Single mounting flange on one end of the motor/gearbox, used for belt drives or direct coupling to another device; (3) B14 (Flange-mounted, both faces): Mounting flanges on both ends, typically for compact in-line installations where motor mounts on one end and load on the other. Gearbox mounting must match motor mounting for proper alignment. Verify both motor and gearbox have the same IEC code before purchasing.

How do I choose between mounting types?

Selection depends on: (1) Space constraints—flange mount for compact installations; foot mount if space is abundant; (2) Torque magnitude—shaft-mounted for heavy-duty high-torque; (3) Maintenance accessibility—foot mount for easy access; flange mount if space-constrained; (4) Alignment requirements—flange or shaft mount for precision; foot mount allows flexibility; (5) Cost—foot mount is cheapest; flange and shaft mounts are premium; (6) Vibration control—flange mount offers best rigidity; foot mount requires good foundation isolation. Most industrial machinery uses foot-mounted or B5 flange-mounted with torque arm for vibration control. Consult your gearbox supplier for specific mounting recommendations.

Installation Guide April 8, 2026 • 6 min read

Gearbox Mounting Types Explained — Foot, Flange, Shaft & Torque Arm

Gearbox mounting method affects alignment, vibration control, maintenance accessibility, and cost. Selecting the correct mounting style for your application ensures reliable operation, minimizes downtime, and optimizes gearbox life. This guide explains the four primary mounting approaches and when to use each.

Foot-Mounted (IEC B3)

Foot-mounted gearboxes rest on four rigid feet bolted to a foundation (floor, frame, or bedplate). The horizontal shaft is typically the output, and the housing base provides mounting surface.

Advantages:

Lowest cost option
Flexible positioning—can be relocated if foundation is modified
Easy maintenance access to all sides
Works with existing floor or frame without modification

Disadvantages:

Vibration transmission to foundation (feet conduct vibration like loudspeaker)
Requires perfectly level, rigid foundation; misalignment if foundation deflects
Output torque creates torsional reaction force; torque arm required for high-torque applications
Less compact than flange mount

When to Use: Small-to-medium duty applications (conveyors, mixers, fans) where space is available and cost is a factor. Always use vibration isolators (elastomeric pads) under feet to decouple vibration from building structure.

Flange-Mounted (IEC B5 and B14)

The gearbox bolts directly to a flat mounting surface (motor flange, driven equipment flange, or structural plate) via bolt holes on the housing face.

B5 (Single Flange): Mounting surface on one face only. Typical for belt drives or coupling to a separate motor.

B14 (Dual Flange): Mounting surfaces on both faces. Used for in-line compact designs where motor mounts on one end and load on the other.

Advantages:

Highest rigidity and alignment accuracy (motor and gearbox are axially concentric)
Compact installation—minimal footprint
No coupling (direct flange-to-flange) saves cost and maintenance
Eliminates vibration transmission to foundation (forces react through flange bolts)
Output torque is reacted through bolted connection, not foundation

Disadvantages:

Higher cost (flange adds manufacturing complexity)
Less flexible—gearbox location is fixed by flange position
Difficult maintenance access (cannot be easily removed without disturbing motor or load)
Requires matching flange on motor or driven equipment

When to Use: Industrial machinery where precision, compactness, and low vibration are critical. Standard for packaging equipment, motors, and space-constrained installations.

Shaft-Mounted

The gearbox mounts directly on the output shaft of the load (e.g., conveyor drum, fan impeller). The gearbox input accepts motor coupling, output is integrated into the load assembly.

Advantages:

Eliminates separate coupling, reducing cost and parts count
Ultra-compact; gearbox and load are combined assembly
Superior alignment (gearbox is co-axial with load)
Reduced inertia and vibration (fewer connections)

Disadvantages:

Load shaft must be robust to carry gearbox weight and radial/axial loads from gearbox bearings
Requires custom-designed shaft and mounting interface
Not interchangeable—gearbox is application-specific
Difficult to replace gearbox without redesigning load assembly

When to Use: Heavy-duty conveyor drives, mixer drives, and rotating equipment where space is critical and load shaft is robust enough to carry gearbox.

Torque Arm

A rigid bracket bolted to the gearbox housing that reacts output torque to the foundation. Essential for preventing gearbox rotation around the motor axis.

How It Works: Output torque tries to rotate the gearbox around the motor centerline. Without a torque arm, the gearbox twists, straining output shaft bearings and couplings. The torque arm is rigidly fastened to both the gearbox and foundation, resisting this twisting motion.

When Required:

All foot-mounted applications with output torque >500 N-m
Loosely-mounted foot-mounted gearboxes (not rigidly bolted)
Hoists and lifts (high torque, safety-critical)
Belt-driven applications with high tension

Design Consideration: Torque arm must be rigidly supported by the foundation or structural frame. A flexible or springy support defeats the purpose. Typically, torque arm is bolted with heavy anchor bolts to the concrete foundation or welded to a steel frame.

Selecting Mounting Type for Your Application

Criteria:

Space Constraints: Compact = flange or shaft mount; spacious = foot mount
Torque Level: High torque = torque arm required; low torque = no arm needed
Vibration Sensitivity: Low vibration required = flange mount; moderate = foot mount with isolators
Alignment Precision: High precision = flange or shaft mount; flexible = foot mount
Maintenance Access: Easy access = foot mount; limited space = flange mount
Cost: Budget-conscious = foot mount; premium = flange or shaft mount

IEC Mounting Codes Summary

B3: Foot-mounted, horizontal shaft, vertical legs

B5: Flange-mounted, single face mounting, horizontal or vertical shaft orientation options

B14: Flange-mounted, dual face mounting, in-line compact configuration

Verify that both your motor and gearbox share the same IEC code (e.g., both B5) for proper compatibility.

Conclusion

Mounting choice is as important as the gearbox specification itself. Foot-mounted is cost-effective for flexible applications but requires good foundation and vibration isolation. Flange-mounted offers superior rigidity and compactness for precision machinery. Shaft-mounted is ideal for integrated conveyor and heavy-duty applications. Always use appropriate torque arm for high-torque applications to prevent gearbox rotation and bearing overload. Anand Gears manufactures gearboxes in all mounting styles; consult our engineers to specify the optimal mounting for your application.

For mounting guidance or custom-mounting design, contact Anand Gears at +91 98203 83719 or anandgears@gmail.com.

Gearbox Mounting Types Explained — Foot, Flange, Shaft & Torque Arm

Foot-Mounted (IEC B3)

Flange-Mounted (IEC B5 and B14)

Shaft-Mounted

Torque Arm

Selecting Mounting Type for Your Application

IEC Mounting Codes Summary

Conclusion

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