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

The MT Series from Apex Coupling offers a comprehensive range of polyurethane spider inserts from MT1 to MT13, covering torque capacities from 22.4 to 2500 N·m. This guide explains how to select the right MT spider for your application.

1. What Is a Spider Insert?

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

• Transmits torque from one hub to the other through the flaps

• Absorbs shock loads and dampens vibration

• Compensates for misalignment – angular, parallel, and axial

• Protects equipment – acts as a fuse, failing before connected components

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

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

2. Why Polyurethane Over Rubber?

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

3. MT Series – Model Range Overview

The MT series covers a wide range of sizes from light to heavy-duty applications:

💡 The number of flaps increases with size – providing more torque transmission capacity for larger applications.

4. Key Selection Criteria

When selecting an MT spider insert, consider these factors:

Step 1: Identify your coupling size

• Measure the outer diameter, inner diameter, and thickness of your existing spider

• Match to the MT series dimensions (MT1 to MT13)

Step 2: Determine torque requirements

• Calculate the torque your application requires

• Select a spider with rated torque ≥ your requirement

• MT series covers 22.4–2500 N·m 

Step 3: Consider operating environment

• Temperature: MT series operates -40°C to +100°C 

• Oil exposure: Polyurethane is oil-resistant 

• Chemical exposure: Polyurethane offers good chemical resistance

Step 4: Select Shore hardness

• Standard: 95A ±5 (90–98 Shore A) 

• Softer (80-92A): Better damping, lower torque capacity

• Harder (95-98A): Higher torque capacity, less damping

5. Shore Hardness Selection – Match Your Application

💡 Standard MT series spiders are typically 95A ±5 – offering the best balance of damping and torque capacity for most applications .

6. Applications Where MT Spiders Excel

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

• Model: MT1 to MT13 – match your coupling size

• Material: Polyurethane – 3-5x longer life than rubber

• Hardness: 90-98 Shore A – standard 95A ±5

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

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

• Oil resistance: Excellent – suitable for oil-exposed environments

• Application: Excavators, compressors, pumps, conveyors, CNC, mining

10. Conclusion

The MT series polyurethane spider insert from Apex Coupling offers superior performance compared to rubber spiders – with 3-5x longer service life, excellent oil resistance, superior wear resistance, and wider temperature range. With MT1 to MT13 sizes covering 22.4–2500 N·m torque capacity, there is a spider to suit every plum/jaw coupling application.

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