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Sprag Clutch Rotations: Backstopping, Indexing, and Overrunning

A sprag clutch rotates in one direction and prevents rotation in the opposite direction.

There are three ways a sprag clutch helps support and control an applications movement:

  • Backstopping
  • Indexing
  • Overrunning

Backstopping Clutch

Diagram indicating clamping direction of a GMN sprag clutch. There are arrows pointing clockwise on the outer part of the clutch, and arrows pointing counter-clockwise on the inside of the clutch

A backstop clutch is commonly used for safety precautions.

If a machine malfunctions, the backstopping clutch is designed to hold the load it’s carrying. A good example is an industrial winch. When it’s lifting and moving a heavy object, it needs to hold that object until it’s ready to be lowered. A winch clutch is an important component located inside the winch that locks the motor shaft to the brake assembly preventing the spool from unwinding when the motor stops.

Our GMN FE 8000 sprag clutch is a great choice because it has no RPM limits and a high torque capacity. For heavy-duty applications, our RA series hold-back clutch is also a good choice.


Backstopping Clutch Application Examples:

  • Conveyors & Winches: Stop Loads
  • High Voltage Switching: Safety Device
  • Textile Machine: Material Feed Protection
  • Industrial Fan: Motor Protection

Indexing Clutch

Diagram indicating clamping direction of a GMN sprag clutch. There are arrows pointing counter-clockwise on the outer part of the clutch, and arrows pointing clockwise on the inside of the clutch

An indexing clutch pushes motion in a circular direction and then allows it to idle or stop.

A good example is a production line that moves to one position then stops, waits, and then moves one position over. This motion is controlled, deliberate, and guided by a one-way sprag clutch.

An indexing sprag clutch can also be an added safety precaution in case of a motor or electrical failure.

Indexing Clutch Application Examples:

  • Printer: Industrial
  • Copiers: Paper Feeding
  • Furniture Production: Glue Roller
  • Food Production: Bottling Plant
  • Sewing Machines: Material Feeder
  • Automatic Winch: Controlled Raising/Lowering

Overrunning Clutch

An overrunning clutch allows the rotating component to spin faster than the actual driving component that is producing the force. An overrunning clutch allows idle spinning to keep going without the engagement of force, bicycle pedals are a good example of how an overrunning clutch works.

Typically, an overrunning clutch engages and disengages when the driven RPM exceeds the driving component’s RPM.

Examples of an Overrunning Clutch:

  • Torque Converters
  • Conveyors: Speed Compensation
  • Mixers: Motor Protection
  • Motorcycles: Gear Box or Automatic Transmissions
  • Packaging Machine: Spins Down Freely
  • Printing Press: Ink Roller Drive

A Critical Component

A sprag clutch supports many different applications to help control movement the momentum. It’s a vital component of many machines and without it the application would not work correctly.

Our Sprag Clutch Product Line

Quality matters when choosing a sprag clutch. GMN has been manufacturing precision components, like a one-way sprag clutch, since 1908.

If you need a one-way sprag clutch, we have three main product lines that are good for backstopping, indexing, or overrunning:

  • Complete Sprag Clutch Units: Designed for big loads with a high torque requirement. Manufactured with both roller bearings and ball bearings. This is our most robust product line.
  • Ball Bearing Sprag Clutch Units: Good for most application requirements (sizes are matched to radial bearings). This is our most popular sprag clutch product line.
  • Sprag Clutch Elements: Made for mounting on shafts without needing to use adapters, lock-nuts or shoulders. Elements consist of a cage, a spring, and sprags.

We offer the highest quality of manufactured precision components and would love the opportunity to quote your next project.

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