Spider inserts (also called coupling cushions, elastomeric spiders, or plum blossom pads) are the heart of jaw/plum couplings – transmitting torque, absorbing shock, dampening vibration, and compensating for misalignment. Choosing the right spider material, series, and hardness is critical for coupling performance, service life, and maintenance costs.

This guide explains the differences between ML, MT, GR, GS, and HRC series, how to select the right spider for your application, and key factors to consider.

1. What Is a Spider Insert (Coupling Cushion)?

A spider insert is the flexible element that fits between the two hubs of a jaw/plum coupling. It:

• Transmits torque from one hub to the other through the spider arms

• Absorbs shock loads and dampens vibration

• Compensates for misalignment – angular, parallel, and axial

• Eliminates metal-to-metal contact – reducing wear and noise

• Defines the characteristics of the entire drive system

The spider is the wear element – designed for easy and cost-effective replacement without moving the hubs or disconnecting the shafts.

2. Spider Series Overview – ML, MT, GR, GS, HRC

3. Polyurethane vs Rubber – Why Choose PU?

✅ Polyurethane is the superior choice for demanding applications – longer life, better wear resistance, superior oil resistance, and wider temperature range.

4. How to Select the Right Spider Insert

Step 1: Identify Your Coupling Type

• Check the coupling nameplate or documentation for the series (ML, MT, GR, GS, HRC) and model number.

• This determines the required spider series and size.

Step 2: Measure the Spider Dimensions (if replacing)

• Measure the outer diameter, inner diameter, and thickness of the old spider.

• Match these dimensions to the specification tables for your series.

Step 3: Select Shore Hardness

• 80 Shore A – Maximum damping, vibration isolation

• 92 Shore A – General purpose, good damping

• 95 Shore A – Higher torque capacity, moderate damping

• 98 Shore A – Maximum torque capacity, high stiffness

💡 Standard hardness for most applications is 92-95 Shore A.

Step 4: Consider Operating Conditions

• Temperature: Verify the spider operates within -40°C to +100°C.

• Oil exposure: Polyurethane is oil-resistant – ideal for oil-exposed environments.

• Shock loads: Polyurethane provides excellent shock absorption.

Step 5: Consider Special Requirements

• Higher torque: Consider 95-98 Shore A hardness.

• Higher damping: Consider 80-92 Shore A hardness.

• Custom sizes: Non-standard dimensions available on request.

5. Applications Where Each Series Excels

6. KTR Rotex Replacement – GS Series

The GS series is a direct replacement for KTR Rotex elastomer. Key features include:

• Straight center of the spider tooth – provides higher stiffness due to coupling prestress

• Crowning of the ends of the spider legs – allows for misalignment

• Curved jaws and solid spider center – provide high-speed capability

• Zero-backlash – preloaded spider design

✅ Choose GS series for KTR Rotex replacement applications requiring zero backlash and high-speed capability.

7. Real‑World Example – Mining Conveyor Upgrade

A mining company was experiencing frequent failure of rubber spider inserts on heavy-duty conveyors. The rubber spiders degraded due to oil contamination and high operating temperatures – requiring replacement every 2-3 months.

They switched to Apex Coupling MT series polyurethane spiders (MT8, 95 Shore A, polyurethane material). Results:

• Service life extended to 12+ months – 4-6x longer than rubber

• Oil degradation eliminated – polyurethane’s oil resistance

• High temperature tolerance – withstood operating temperatures up to 80°C

• Downtime reduced – fewer replacements

• Maintenance costs reduced – no lubrication required

8. Installation & Maintenance Tips

1. Inspect the spider – Check for cracks, wear, or deformation at planned maintenance intervals

2. Clean the hubs – Remove debris before installing a new spider

3. Install the spider – Fit between the two hub jaws – ensure proper engagement

4. No lubrication required – Spider is self-lubricating

5. Replace when worn – Don’t wait for complete failure

6. Match hardness to application – Softer for damping, harder for torque

9. Selection Checklist

• □ 

  Series: ML, MT, GR, GS, or HRC – match your coupling type

• □ 

  Model: ML1-ML13, MT1-MT10, GR19-GR100, GS19-GS75, HRC70-HRC280

• □ 

  Material: Polyurethane – oil & wear resistant, 3-5x longer life than rubber

• □ 

  Hardness: 80-98 Shore A – match your torque and damping requirements

• □ 

  Temperature: -40°C to +100°C – verify operating range

• □ 

  Oil resistance: Excellent – suitable for oil-exposed environments

• □ 

  Torque: 22.4–2500 N·m – ensure it exceeds your requirement

• □ 

  KTR Rotex replacement: Choose GS series

10. Conclusion

The ML, MT, GR, GS, and HRC series polyurethane spider inserts from Apex Coupling offer superior performance compared to rubber spiders – with 3-5x longer service life, excellent oil resistance, superior wear resistance, and wider temperature range. With a comprehensive range of sizes and hardness options, there is a spider to suit every jaw/plum coupling application.

👉 Need a spider insert for your coupling? Contact us with your series, model, and hardness requirements.