Introduction to Inline Gear Reducers

August 3, 2023

Gear design and performance characteristics directly impact how well the gearbox can meet your application's needs. In this post, we'll walk through a basic introduction to inline gearboxes and some typical applications. It can be challenging to find the right inline gearbox for specific applications, so consult with an expert if you still have questions after reading this post.

What Does Inline Mean?

An inline gearbox's input and output shafts have the same orientation, even though they may or may not offset each other. An inline gearbox transmits torque in the same direction as the motor, unlike different gearbox configurations where the gearbox output shaft may be at right angles to the input shaft.

Inline gearboxes are categorized as parallel or coaxial type, each of which uses different gear systems that offer distinct sets of strengths and weaknesses.

Parallel Inline Gearboxes

A parallel inline gearbox’s input and output shafts are oriented in the same direction but are offset by some distance, resulting in the shaft axis being parallel to each other. Parallel gearboxes typically use spur, helical, or double helical gear systems.

Spur Gears

A spur gear is the simplest gear type, with straight teeth projecting radially from the gear center. While they are relatively low-cost, spur gear systems suffer from high noise, high backlash, and relatively low torque transmission capability. Because of the limited gear tooth surface area, the teeth suffer from high stresses, and this gear system uses relatively low-speed and low-torque applications.

Helical Gears

Helical gears have teeth that run diagonally, increasing the meshing surface area between gear teeth and the number of teeth in contact, consequently increasing the amount of torque the gearbox can handle. While helical gears have better all-around performance characteristics than spur gears, with far higher torque capability and somewhat quieter operation, they produce thrust forces along the shaft axis that can put significant stress on bearings. Depending on the amount of pressure, this sometimes requires unique approaches to withstand the load, and their power transmission capacity is limited compared to double helical gears.

Double Helical Gears

Helical gears produce thrust force that can affect gearboxes' life span. Double helical gears use a gear that resembles two opposing helical gears placed side-by-side to deal with the thrust force produced. Double helical gear systems double the helical gears' high torques without thrust forces while maintaining helical gears' benefits.

Parallel Inline Gearbox Applications

Because of their relatively simple gear design and large size, parallel gearboxes typically are used in low-cost, high torque applications where saving space is not a priority. Their larger surface area corresponds to better heat dissipation, enabling them to operate in hotter industrial environments, and they offer good efficiency and substantial reduction ratios.

Parallel gearboxes are used in every industrial task, operating large and small machinery across many different industries.

Coaxial Inline (Planetary) Gearboxes

A coaxial inline gearbox’s input and output shafts are oriented along the same line with no position offset, enabling the motor, gearbox, and load to rotate around the same axis. These gearboxes use planetary gear systems.

A planetary gear system is a relatively complex gear design that uses a set of gears (called 'planet' gears), which rotate around a single gear at the center (the 'sun' gear). This gear arrangement allows a large amount of torque to be transmitted along a straight axis with perfect balance, enabling high reduction ratios in a compact size. Planetary gearboxes can be easily connected in stages to achieve high reduction ratios, and their low backlash makes them ideal for increased acceleration and high precision applications.

Planetary Gearbox Usage

Planetary gearboxes are ideal for applications requiring high torque in a compact package. Their low backlash, high efficiency, and exceptional performance compared to most other gear types put them at the top of the list for any task where performance is paramount.

They have very few downsides. Because of their smaller surface area, planetary gearboxes have reduced heat dissipation capability, and their relative complexity typically makes them slightly more costly and reduces their ease of maintenance.

Various industrial machinery applications use planetary gearboxes, where the highest priority is to reduce size and weight while maximizing efficiency.


Now that you have an in-depth understanding of inline gearboxes and the different gear systems they use, you can match their strengths and weaknesses to your application's specific requirements to find the gearbox that is right for you.

Start building your ideal gearbox right away with our Gear Reducer Builder, or get in touch to speak to our experienced team today.

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