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How to Read a Gearbox Nameplate: Ratio, Torque, Speed and Mounting Position
Views: 0 Author: Site Editor Publish Time: 2026-07-31 Origin: Site
A gearbox nameplate may be small, but it contains the essential information required to identify, install, operate, and replace an industrial gearbox. For maintenance teams, equipment manufacturers, distributors, and purchasing managers, reading a gearbox nameplate correctly can prevent wrong output speeds, insufficient torque, lubrication problems, and expensive machine modifications.
The most important gearbox nameplate data normally includes the gearbox model, gear ratio, input speed, output speed, rated output torque, service factor, mounting position, serial number, and lubrication information. On a complete gearmotor, the electric motor has a separate nameplate showing power, voltage, frequency, rated speed, efficiency, protection class, and duty.
This guide explains how to read gearbox ratio, torque, speed, and mounting position, how these values relate to one another, and what to confirm when selecting a replacement gearbox or gearmotor.
Why the Gearbox Nameplate Matters
The gearbox nameplate is often the fastest source of technical information when the original catalog or equipment manual is unavailable. It helps users:
Identify the gearbox series and frame size
Confirm the gear ratio and output speed
Check rated output torque
Determine the mounting position
Verify the motor and gearbox combination
Find an equivalent gearbox from another manufacturer
Avoid selecting a replacement by appearance or motor power alone
A correct gearbox replacement must provide the required speed and torque while fitting the existing shaft, flange, base, or hollow-shaft connection. Two gearboxes using the same motor power can have very different ratios, capacities, and dimensions.
Main Information on a Gearbox Nameplate
Manufacturer, Series, and Model
The manufacturer name or logo identifies the original brand. The model code may describe the gearbox type, housing size, reduction stage, shaft arrangement, motor frame, and mounting design.
A model such as R87-DRN112M4-i=24.99-M1 may indicate:
R: inline helical gearbox series
87: gearbox housing size
DRN112M4: motor series, frame, and pole number
i=24.99: gear ratio
M1: mounting position
Other common codes include K77, F87, S67, NMRV090, XWD4, or BLD5. However, model letters and size numbers are manufacturer-specific. An “87” housing from one brand is not automatically dimensionally identical to an “87” from another.
When replacing a gearbox, use the model code together with ratio, torque, mounting position, shaft dimensions, and installation measurements.
Serial Number or Order Number
A serial number, production number, or order number may connect the gearbox to the manufacturer’s original records. Those records can contain the exact gear set, bearings, seals, motor adapter, lubricant, shaft design, and special modifications.
The serial number can also distinguish a standard model from a customized unit. Photograph both nameplates and the gearbox from several angles.
How to Read the Gear Ratio
What Does Gear Ratio Mean?
The gear ratio may appear as:
i = 10
i = 25.6
Ratio 30:1
Reduction ratio 40
For a reduction gearbox, a ratio of 30:1 means the input shaft turns approximately 30 times for each output shaft revolution.
The basic relationship is:
Output speed = Input speed ÷ Gear ratio
If a motor runs at 1450 rpm and the gearbox ratio is 25:
1450 ÷ 25 = 58 rpm
The estimated gearbox output speed is therefore 58 rpm.
Why the Actual Output Speed Can Differ
Use the motor’s rated speed rather than its synchronous speed. A four-pole motor at 50 Hz has a synchronous speed of 1500 rpm, but its rated speed is commonly around 1430–1470 rpm because of motor slip. At 60 Hz, a four-pole motor may be rated around 1720–1770 rpm rather than exactly 1800 rpm.
Actual output speed is affected by:
Rated motor speed
Supply frequency
Number of motor poles
Gear ratio
Motor slip
VFD frequency
Mechanical load
A small speed difference may be acceptable in some conveyors, but it can affect mixers, dosing equipment, elevators, and synchronized production machinery.
Ratio Does Not Identify Gearbox Type
Similar ratios can be produced by helical, helical-bevel, worm, and cycloidal gearboxes. Selection also depends on efficiency, torque, space, duty, shaft direction, and load.
How to Read Input and Output Speed
Input Speed
The input speed is the rotational speed entering the gearbox. On a direct-coupled gearmotor, it is normally the motor shaft speed.
Some gearbox nameplates show maximum permissible input speed instead of actual operating speed. A maximum value is a mechanical limit, not necessarily the recommended continuous operating point.
Input Speed with a VFD
A variable frequency drive changes motor and gearbox input speed. Higher frequencies can increase bearing speed, oil temperature, noise, and mechanical stress. Low-frequency operation may reduce motor cooling unless an independent cooling fan is used.
For continuous VFD operation, confirm the permitted gearbox speed range and the motor’s cooling arrangement.
Output Speed
Output speed may be marked as n2, output rpm, or r/min. It directly affects machine performance and production speed.
If the gearbox nameplate is damaged, output speed can be estimated from rated motor speed and ratio. It can also be measured with a tachometer when the machine can be operated safely.
How to Read Gearbox Torque
Rated Output Torque
Output torque may appear as M2, T2, rated torque, or output torque, usually in Nm or kNm. For example, M2 = 850 Nm means the gearbox is rated to transmit approximately 850 newton-metres under the manufacturer’s specified conditions.
Do not confuse the following values:
Actual application torque
Calculated transmitted torque
Rated continuous gearbox torque
Maximum permissible torque
Short-duration peak torque
Starting torque
A gearbox should be selected according to operating duty, not just a single torque value.
Calculating Approximate Output Torque
Approximate output torque can be calculated as:
Output torque (Nm) = 9550 × Motor power (kW) × Gearbox efficiency ÷ Output speed (rpm)
For a 5.5 kW motor, 58 rpm output speed, and 94% efficiency:
9550 × 5.5 × 0.94 ÷ 58 ≈ 851 Nm
This is the approximate output torque when the motor operates at full rated power. The selected gearbox should have sufficient rated torque after the application service factor is considered.
Efficiency Affects Available Torque
Gearbox efficiency varies by design. Helical, parallel shaft helical, and helical-bevel gearboxes generally provide high efficiency. Worm gearboxes can have lower efficiency, especially at high reduction ratios. Cycloidal reducers provide compact high-ratio transmission and strong overload resistance, but their rated torque must still be checked.
Calculating torque from motor power without considering efficiency can overestimate the usable output torque.
Maximum Torque Is Not Continuous Torque
Maximum torque may be a structural or short-duration limit, not a continuous rating. For mixers, crushers, lifting machines, and frequently started conveyors, confirm both continuous and peak torque.
How to Read the Service Factor
What Is Service Factor?
Service factor may be marked SF, fs, or service factor. It represents the operating margin between the gearbox capacity and the expected application load.
A service factor of 1.0 means the gearbox is used near its nominal rating under defined conditions. A value of 1.5 provides more capacity margin.
Required service factor depends on:
Operating hours per day
Starts per hour
Uniform, moderate, or heavy shock load
Driven machine type
Reversing or braking
Ambient temperature
Load inertia
Reliability requirement
Because manufacturers may calculate service factor differently, compare torque and duty data rather than only the SF number.
Mechanical and Thermal Capacity
A gearbox can have sufficient mechanical torque capacity but still overheat. Thermal capacity becomes important during continuous operation, at high ratios, in hot environments, or where airflow is restricted.
The supplier may need to check input power, speed, operating hours, ambient temperature, mounting position, oil type, and ventilation.
How to Read the Mounting Position
Why Mounting Position Is Critical
The gearbox mounting position describes how the unit is installed relative to gravity. It affects shaft orientation, oil level, breather location, bearing lubrication, and sometimes internal construction.
Common codes include M1, M2, M3, M4, M5, and M6. Their meanings can vary by gearbox manufacturer and series. Never assume that M1 from one brand is identical to M1 from another without checking the mounting diagram.
Common Gearbox Mounting Arrangements
Gearboxes may be:
Horizontal foot mounted
Vertical shaft up
Vertical shaft down
Flange mounted
Hollow shaft mounted
Torque-arm mounted
Ceiling or side mounted
Foot-Mounted Gearbox
A foot-mounted gearbox is bolted to a base through the housing feet. The mounting surface should be flat and rigid to avoid housing distortion, vibration, and shaft misalignment.
Flange-Mounted Gearbox
A flange-mounted gearbox connects directly to the driven machine. The flange outside diameter, bolt circle, pilot diameter, bolt-hole size, and output shaft must be verified.
For vertical installation, clearly state whether the output shaft points upward or downward.
Hollow-Shaft and Torque-Arm Gearbox
A hollow-shaft gearbox mounts onto the driven machine shaft and may use a key, shrink disc, spline, or locking device. A torque arm prevents the gearbox housing from rotating.
For replacement, confirm hollow-shaft diameter, keyway, insertion length, torque-arm position, and available installation clearance.
Mounting Position and Lubrication
Changing from horizontal to vertical installation may require a different oil quantity, relocated plugs, extra bearing lubrication, or different seals.
Operating in an unapproved mounting position can cause leakage, overheating, bearing damage, and oil starvation.
Other Important Gearbox Nameplate Data
Motor Power and Motor Data
A gearmotor includes both gearbox and motor information. The motor nameplate normally shows power, voltage, frequency, rated current, rated speed, efficiency, power factor, duty, IP class, insulation class, and connection.
Motor power alone cannot identify the correct gearbox. The same motor can be combined with several gearbox sizes and ratios.
Lubricant Type and Oil Quantity
The gearbox nameplate may specify oil viscosity, lubricant category, or fill quantity. Mineral, synthetic, and food-grade lubricants may not be compatible with one another. Consult the gearbox supplier before mixing or changing oil.
Direction of Rotation and Backstop
Many gearboxes operate in both directions, but a backstop permits only one direction. Confirm rotation before startup. Incorrect rotation can stop the machine or damage connected equipment.
Step-by-Step Gearbox Nameplate Checklist
Step 1: Record the Complete Model
Copy every letter, number, and suffix. A small suffix may indicate a special flange, shaft, brake, backstop, or mounting position.
Step 2: Confirm Ratio and Speed
Find the ratio marked “i” and compare input speed, output speed, and motor rated speed. Check that the values are mathematically consistent.
Step 3: Identify Torque and Service Factor
Record rated output torque and determine whether it is continuous, nominal, or maximum. Review the service factor against the actual machine duty.
Step 4: Confirm Mounting Position
Check the original manufacturer’s mounting diagram. Verify shaft direction, terminal-box position, and oil-plug arrangement.
Step 5: Measure Installation Dimensions
Record:
Solid or hollow output shaft dimensions
Keyway size
Flange and pilot diameter
Bolt circle and hole size
Foot-hole spacing
Shaft center height
Torque-arm position
Motor interface
Step 6: Confirm the Application
Provide the driven machine, daily operating hours, starts per hour, load type, ambient temperature, reversing duty, and any shock load.
Common Gearbox Nameplate Mistakes
Selecting by Motor Power Only
Motor power does not define ratio, output speed, torque capacity, or gearbox size.
Confusing Ratio with Output Speed
A ratio of 30 does not mean 30 rpm. Output speed depends on input speed.
Assuming Mounting Codes Are Universal
Always check the manufacturer’s mounting-position drawing.
Ignoring Gearbox Efficiency
Different gearbox designs can produce different usable torque from the same motor power.
Treating Peak Torque as Continuous Torque
Peak or maximum torque is not automatically suitable for continuous operation.
Changing Orientation Without Changing Lubrication
Oil quantity and plug positions may need to change when the mounting position changes.
Ignoring Installation Dimensions
A technically suitable gearbox may still require costly machine modifications if the shaft, flange, or center height does not match.
How Victory Supports Gearbox Selection and Replacement
Victory Machinery Technology Co., Ltd. supplies industrial gearboxes, gearmotors, and IEC electric motors for OEM equipment builders, distributors, maintenance companies, and industrial users.
Three-phase, single-phase, brake, VFD, and explosion-proof gearmotors
Gearbox Replacement and Brand-Equivalent Support
When the original gearbox is unavailable, discontinued, or too expensive, Victory can evaluate a replacement from the nameplate, ratio, output speed, torque, mounting position, dimensions, and application duty.
Dimensional Matching
Victory can review the output shaft, hollow shaft, flange, center height, mounting holes, torque arm, and motor interface. A standard model is recommended whenever possible; customized dimensions can be evaluated when a direct fit is required.
Options include custom voltage and frequency, shafts, flanges, mounting positions, paint, private-label nameplates, bearings, PTC/PT100 sensors, heaters, and terminal boxes.
Victory has 22 years of manufacturing experience and supports sample orders, batch production, OEM projects, technical drawings, quality inspection, CE and ISO9001 documentation, and an 18-month warranty.
Information Needed for a Replacement Gearbox
For an accurate replacement recommendation, provide:
Gearbox nameplate photo
Motor nameplate photo
Gearbox photos from several angles
Motor power and rated speed
Gear ratio or required output speed
Output torque, if known
Mounting position
Shaft or hollow-shaft dimensions
Flange and mounting dimensions
Application and operating duty
FAQ About Reading a Gearbox Nameplate
What does “i” mean on a gearbox nameplate?
The letter “i” normally indicates the gear ratio. For example, i = 25 means the input shaft turns about 25 times for each output shaft revolution.
How do I calculate gearbox output speed?
Divide rated input speed by gear ratio. A 1450 rpm motor with a 25:1 gearbox produces approximately 58 rpm.
What does M2 mean on a gearbox nameplate?
M2 usually means rated output torque in Nm. Confirm whether the listed value is continuous, nominal, or maximum torque.
Can I replace a gearbox with another brand using the same ratio?
Yes, but ratio alone is insufficient. Torque, service factor, mounting position, shaft and flange dimensions, thermal capacity, and application duty must also match.
Is gearbox mounting position important?
Yes. It affects oil level, lubrication, breather position, bearing lubrication, and shaft orientation. The wrong mounting position may damage the gearbox.
What if the gearbox nameplate is unreadable?
Send photos, motor data, shaft and mounting dimensions, and application details. Ratio can also be estimated by measuring input and output speed.
Can a gearbox operate at a different input speed?
Sometimes, but the permitted speed range must be confirmed. Higher speeds increase heat and noise, while low-speed VFD operation may require independent motor cooling.
What Data Is Most Important for Initial Selection?
Start with motor power and either gear ratio or required output speed. Then confirm torque, mounting position, dimensions, and duty cycle.
Conclusion
Knowing how to read a gearbox nameplate makes selection, troubleshooting, and replacement faster and more reliable. The key fields are gearbox model, gear ratio, input speed, output speed, rated output torque, service factor, and mounting position.
These values must be considered together. Matching only motor power or ratio can result in incorrect machine speed, insufficient torque, overheating, lubrication failure, or installation incompatibility.
Record the gearbox nameplate, motor nameplate, mounting position, and key dimensions before requesting a replacement. Victory can then help evaluate a compatible helical gearbox, worm gearbox, cycloidal reducer, or complete gearmotor solution for the application.
