Technical Foundation
What Is a Jaw Coupling Hub?
A jaw coupling connects two shaft ends by mounting a hub on each shaft — each hub has integral jaws that mesh with a soft elastomeric spider sandwiched between them — so torque transmits from one shaft to the other through compression of the spider's lobes rather than through a rigid metal-to-metal connection. This design gives the coupling a limited but useful amount of misalignment tolerance and shock/vibration dampening, since the elastomer absorbs sudden torque spikes and minor angular or parallel shaft misalignment that a rigid coupling would transmit directly into the connected equipment's bearings.
Hub sizing follows standardized series (commonly the L-series: L050, L070, L090, L095, L099, L100, L110, L150, L190, L225) where each size number corresponds to a specific bore range, jaw dimension, and rated torque capacity, and metric-bore hubs are also available within the same series for shafts sized in millimeters. Both hubs in a coupling must be the same series to mate correctly (an L100 hub will not mesh with an L095 spider or hub), but the two hubs can have different bore sizes if the driving and driven shafts are different diameters, since bore size is independent of jaw geometry within a given series.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Hub Series | L050 through L225 (L-series standard sizes) | Determines jaw geometry and torque rating; both hubs in a coupling must share the same series |
| Bore Size | Sized independently per hub to each shaft diameter | The two hubs on a coupling can differ in bore size as long as both match the same series |
| Hub Material | Aluminum, sintered iron, steel | Aluminum for light duty/low inertia; sintered iron and steel for higher torque and duty cycles |
| Spider Durometer/Material | Urethane, Buna-N, Hytrel in varying hardness | Softer spiders dampen shock/vibration better; harder spiders transmit torque more rigidly with less backlash |
| Mounting Style | Set screw, clamp-style (split hub) | Clamp-style hubs allow removal without axial shaft movement, useful in tight installations |
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Applications
Where Jaw Coupling Hubs Get Used
Jaw couplings are specified anywhere two rotating shafts need to be connected with some tolerance for misalignment and shock absorption.
Pump & Motor Drive Connections
Connecting motor output shafts to pump input shafts while absorbing minor misalignment and startup torque spikes.
Gearbox & Speed Reducer Couplings
Linking gearbox output shafts to driven equipment where shock absorption protects gear teeth from torque spikes.
Conveyor & Material Handling Drives
Coupling drive motors to conveyor gearboxes and rollers across general material handling equipment.
Compressor & Blower Drive Systems
Absorbing torsional vibration between motor and compressor/blower shafts in industrial air systems.
HVAC Fan & Blower Drives
Connecting motor shafts to fan shafts in air handling equipment where vibration dampening extends bearing life.
General Machine Building & OEM Equipment
Standard shaft coupling solution across a wide range of light-to-medium duty rotating equipment.
FAQ
Jaw Coupling Hubs Questions, Answered
Do both hubs in a jaw coupling need to be the same bore size?
No — the two hubs need to match the same series (so the jaw geometry and spider fit correctly), but each hub's bore is sized independently to its own shaft diameter. It's common and normal for a coupling to have different bore sizes on the motor side versus the driven equipment side.
Can I mix hub series, like an L100 hub with an L095 spider?
No — jaw geometry and spider lobe size are matched within a series, so mixing series will either not mesh properly or will mesh with reduced contact area and torque capacity. Always keep both hubs and the spider within the same series.
What does the elastomeric spider actually do, besides transmitting torque?
The spider absorbs shock loads and torque spikes (such as motor startup) and accommodates a limited amount of angular, parallel, and axial shaft misalignment, protecting bearings and gearboxes on both sides of the coupling from vibration and misalignment loads that a rigid coupling would transmit directly. It also acts as a wear/sacrificial component that's far cheaper to replace than the hubs or connected equipment.
How do I choose the spider's durometer (hardness)?
Softer spiders dampen shock and vibration more effectively but have more torsional 'give' (backlash) under load; harder spiders transmit torque more rigidly and precisely with less backlash but pass more vibration through to the connected equipment. High-shock applications like reciprocating compressors typically favor softer spiders; precision-timing applications favor harder ones.
What's the benefit of a clamp-style (split) hub over a set-screw hub?
A clamp-style hub can be installed and removed by loosening clamp bolts without needing to slide the hub axially along the shaft, which matters when there's no room to move connected equipment or when the shaft has a shoulder or other feature blocking axial movement. Set-screw hubs are simpler and lower cost where axial installation clearance isn't a constraint.
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