Spiroid Gearing

Solving the Unsolvable

ITW Heartland is the only partner for custom gears, gearbox design, and precision manufacturing you’ll ever need. For more than 60 years, our unique gearing solutions have served thousands of applications in dozens of industries. Our Spiroid®, Helicon®, Endicon®, and Concurve® gear designs featuring our High Torque to Space Ratio technology (HTSR™) are the solution for any gearing need.

ITW Heartland delivers economy, variety, complete service, and fast turnaround. We serve a variety of markets with specialty applications for:

  • Aerospace

  • Military & Defense

  • Power Generation

  • Transportation

  • Robotics


HTSR – High Torque to Space RatioHigh Torque to Space Ratio - HTSR logo

Conquering big challenges in small spaces.

HTSR™ Gearing (High Torque to Space Ratio) is exclusive to ITW Spiroid. Our designs and gears have been proven in military, aerospace, and industry applications for the past 60 years. HTSR™ Gearing is used in both right angle and inline applications.There are times when traditional gearing methods simply will not provide the power and torque needs required within space or weight limitations. And that is exactly where HTSR™ Gearing will shine.

HTSR™ Gearing is designed to meet difficult application requirements, rather than modifying the application to the limited capability of a gearing method.

HTSR™ Gearing can be applied to all the ITW Spiroid trademarked designs and is used in:

  • Custom gearbox designs
  • Spiroid® and Helicon® gearing
  • Concurve® spur type gearing
  • Endicon® indexing and coupling rings


Spiroid® and Helicon® Gearing

The Spiroid family of gears consists of two trademarked brands, Spiroid® and Helicon®. This type of gearing, often referred to as “skew axis gearing”, operates onSpiroid Gearing non-intersecting and non-parallel axes. Our designs are produced with contemporary software, tooling, and methods developed by ITW. We own and maintain the intellectual property to all of our proprietary gearing technology. The Spiroid family of gears is designed exclusively for right angle power transmission where high torque is required from a small gear set envelope. A variety of materials can be used including steel, brass, aluminum bronze, forgings, powder metal, and plastic (either molded or cut). Typical features include: high torque capability, high stiffness, quiet operation, compact and lightweight design, and easy assembly. Ratios are available ranging from 3:1 to more than 400:1.

The example to the right contrasts Spiroid and Helicon gearing to traditional right angle power transmission methods (bevel gearing and worm gearing).The offset from the gear centerline allows the Spiroid and Helicon gearing to maintain more tooth surface to be in contact at any time, thus increasing the contact ratio. By increasing the contact ratio, higher torque capacity is generated and motion transmission is smoother.


Key Characteristics

  • Simple and positive backlash control – zero backlash in certain cases
  • Right or left-hand gear orientationSpiroid & Helicon Gearing
  • Bi-directional driven gears
  • Adjustable mounting distance based on assembly variation
  • High accuracy for precise positioning or indexing and constant velocity
  • High reduction ratios
  • Superior shock strengthHigh torque capability in relationship to gear set size
  • Quiet operation
  • Material options for the gear desired
  • Compact and lightweight
  • High stiffness
  • Design flexibility to meet the application requirements rather than developing the application requirements to meet the gearing method


Concurve® Gearing

Concurve® gearing is an exclusive version of our HTSR™ gear technology. This innovative gear tooth design is not a typical involute form. The Concurve is a “spur gear”Concurve Gearing with stronger teeth created for the strength and life cycle duty requirements of the United States military and is now available to you. Its primary application is found in parallel axis gear and gearbox designs. You will find a compelling comparison of Concurve gearing to involute gearing below.

Concurve Gearing 2

  • 50% more running time hours at equivalent loads 
  • 50% more torque capacity in the same frame size
  • 33% smaller frame size to achieve equivalent torque capacity 
  • 90% minimum efficiency
  • Low backlash
  • Greater shock resistance due to larger stronger teeth

The unique shape of the Concurve gear tooth is one reason why ITW Heartland achieves continuous torque ratings that are two to six times greater than gearboxes or gear sets using standard involute tooth form in most applications.


Endicon® Couplings

Our Endicon® brand of indexing and face coupling rings are used for inline power transmission where zero backlash and precise location control are required. The twoEndicon Couplings components are mirror images of each other and can transfer very high torque for inline applications.

  • Self-centeringRigid and stiff coupling
  • Very high load transfer capability
  • Indexing calling out less than one degree of true position
  • Accuracies within plus or minus 3 arc seconds
  • Uniform tooth spacing with angular position repeatability of .000050 inch
  • Variable tooth geometry for specific applications
  • Material options for gear selected


An Endicon ring set can be used as a precise indexing device or as a face type coupling. While Endicon rings are useful in many applications, they are particularly valuable for these requirements:

  1. Where space and/or weight limitations do not allow a conventional shaft coupling.
  2. Where keys or splines are not sufficient for the torque load, or require excessive axial clearances for component assembly or disassembly.
  3. Where finite incremental indexing of one member with respect to another is required.
  4. Where quick disengagement is required.Where maximum rigidity is required.
  5. Where positive engagement of two components must also be a common center.


Custom Gearboxes

Custom GearboxesHTSR™ Gearing concepts and designs are used in customized gearboxes around the world. ITW Heartland can design the custom gearing or an entire gearbox for your application. Whether inline, planetary, or right angle, a custom solution can be achieved with our proven design and engineering services.
Outcomes that can be achieved with Custom Gearboxes include:

  • 30-50% more torque a smaller work envelope
  • High efficiency
  • Wide range of gear ratios available during design
  • Near zero backlash capability
  • Application suitability and fit with custom designs
  • Quiet operation
  • Long life duty
  • Lifetime lubrication
  • Coolant exchange design options
Typical uses for ITW Heartland Gear Boxes:

  • Actuators
  • Pumps
  • Fan drives
  • Remote power generation
  • Robotic arms
  • Weapons systems
  • Auger drives
Key Custom Design Options:

  • Ratio Range: Choose from 6:1 to more than 400:1 in Spiroid® and Helicon® gearboxes. No other type of gear system is capable of spanning this range of ratios.
  • Backlash: Choose a near zero backlash design at our standard pricing
  • Configuration: Choose from a solid output shaft, hollow output shaft, dual output shafts, and many more.
  • Special Design Efficiency: Accommodate higher dynamic or self-locking efficiencies with the versatility of Spiroid® and Helicon® gearing
  • Application Considerations: Designs will address space limitations and mounting requirements to meet your specific application requirements.