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SI5 Bearing: Specifications & Selection Essentials
For any application requiring a compact, steel-on-steel rod end bearing with a 5 mm bore and M5 thread, the SI5 series — specifically the SI5E and SI5ES — delivers reliable performance under moderate loads and misalignment. The key decision factor is lubrication: choose SI5E (no lubrication hole) for maintenance-free or intermittent use, and SI5ES (with oil cup) for applications requiring regular relubrication to extend service life. Both versions share the same core dimensions, load ratings, and 13° misalignment capability.
Below are the critical technical specifications for the SI5 bearing (based on UKL Bearing Manufacturing Co., Ltd. manufacturing data). These numbers are the foundation for any selection process.
| Parameter | SI5E / SI5ES | Remarks |
| Bore diameter (d) | 5 mm | Fits 5 mm shaft |
| Width (B) | 6 mm | Overall inner ring width |
| Ball diameter (dK) | 10 mm | Spherical ball size |
| Thread (G 6H) | M5 | Right-hand standard |
| Dynamic load rating (C) | 3.4 kN | Basic dynamic radial load |
| Static load rating (C₀) | 8.1 kN | Basic static radial load |
| Misalignment angle (α) | ≈ 13° | Maximum allowable tilt |
| Weight | ≈ 0.023 kg | Lightweight design |
| Operating temp. | -50°C to +150°C | Steel/steel friction pair |
Key takeaway: Both SI5E and SI5ES share identical load capacities and dimensions. The only functional difference is the lubrication method — which directly impacts maintenance intervals and suitability for continuous or harsh environments.
SI5ES vs SI5E: Which One Fits Your Application?
The core distinction between SI5E and SI5ES lies in lubrication access. This small suffix difference dictates maintenance strategy and long-term reliability. Below is a direct comparison to help you decide.
| Feature | SI5E | SI5ES |
| Lubrication hole / oil cup | None | Yes (via rod end eyelet) |
| Relubrication | Not possible (sealed design) | Periodic relubrication recommended |
| Typical application | Light-duty, low-frequency motion, or where maintenance access is limited | Continuous oscillation, heavy cycling, or outdoor/harsh conditions |
| Durability in dry conditions | Suitable for intermittent use; may wear faster under continuous load | Extended life when regularly greased |
| Standard suffix | SI5E | SI5ES (S = oil groove / lubrication) |
Selection rule: If your mechanism operates under constant motion, heavy shock, or dusty environments, the SI5ES with its lubrication capability is the safer choice. For occasional adjustment, low-cycle positioning, or sealed assemblies, the SI5E offers simplicity and lower maintenance overhead.
Both versions are available with left-hand threads (denoted by “L” in the model, e.g., SIL5ES) for applications requiring reverse thread configurations.
Rod End Bearing Selection Guide: SI5 in Context
Selecting the right rod end bearing goes beyond just bore size. Use this step-by-step decision flow to evaluate the SI5 against your operational requirements.
Five Critical Criteria for SI5 Selection
- Load magnitude: SI5 handles 3.4 kN dynamic and 8.1 kN static. Ensure your peak load stays within these limits, with an appropriate safety margin.
- Misalignment angle: Maximum 13° (≈). Exceeding this will cause edge loading and premature failure. For higher misalignment, consider SI series with larger dK.
- Thread direction: Standard right-hand (no suffix) or left-hand (add “L”). Confirm mating thread direction before ordering.
- Lubrication strategy: As detailed above — choose ES for maintenance-friendly design; E for sealed, no-relube applications.
- Temperature range: -50°C to +150°C covers most industrial environments, but for extreme low/high, consult UKL for special materials.
Always cross-check with the mounting structure: The SI5 has an overall length (I₄) of 40.5 mm and thread length (I₃ min) of 11 mm, which affects rod length calculations.
UKL SI5 Bearing: Precision and OEM/ODM Capability
As a specialized manufacturer, UKL produces the SI5E and SI5ES with strict adherence to dimensional accuracy and material standards. The steel-on-steel sliding pair ensures high wear resistance, while the galvanized surface on the rod end body provides corrosion protection.
- Customization: UKL offers SI5 bearings with special thread pitches or precision grades beyond the standard 6H, meeting specific OEM requirements.
- Quality assurance: Each SI5 batch undergoes dimensional checks, load testing, and surface finish inspection, ensuring consistent performance.
- Supply chain: With over 15 years of export experience, UKL provides reliable lead times for SI5E and SI5ES, supporting both prototype and bulk orders.
UKL has become a trusted partner thanks to its technical precision, flexible OEM services, and highly competitive production scale.
Frequently Asked Questions: SI5 Bearing
Final Technical Recommendation
For most industrial linkages, automation arms, and hydraulic cylinder attachments requiring a 5 mm bore rod end, the SI5ES is the preferred choice due to its lubrication capability and extended service life under dynamic loads. Choose the SI5E only when the mechanism is sealed, maintenance-free, or subjected to very low operating cycles.
Always verify the static load safety factor (C₀ / applied load) — a minimum of 2.0 is recommended for shock-free applications, and higher for vibrating or oscillating movements. The SI5 offers a robust 8.1 kN static capacity, making it suitable for many light-to-medium duty scenarios.
For specific customizations such as left-hand threads, special plating, or non-standard thread lengths, consult UKL’s engineering team to ensure the SI5 variant meets your exact design requirements.
