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R Series
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R2-5 Open Inch Series Miniature Ball Bearing | Ultra-Low Friction & High-Speed Dynamics | 3.175×7.938×2.779mm

R2-5 Open Inch Series Miniature Ball Bearing | Ultra-Low Friction & High-Speed Dynamics | 3.175×7.938×2.779mm

The R2-5 Open is a precision-engineered, inch-dimensional miniature deep groove ball bearing developed specifically for applications demanding absolute minimum rotational resistance. With a standard 1/8" bore diameter, this bearing utilizes an entirely unshielded (open) architecture. By eliminating the physical barriers of shields or rubber seals, the R2-5 Open achieves a zero-contact environment that eradicates frictional drag. This design is highly favored for mechanisms housed within clean, enclosed environments or oil-bath systems, where maximum RPM and rapid heat dissipation are critical for system performance.

R2-5 Miniature Deep Groove Ball Bearing 1/8" × 5/16" × 7/64" | Zero Drag for Maximum Efficiency

Built for internal assemblies where external contamination is already controlled, the R2-5 Open excels in high-speed, low-torque scenarios. Whether it is facilitating the rapid movement of an enclosed stepper motor or providing fluid rotation in a delicate optical assembly, this bearing guarantees responsive and unimpeded motion. The exposed rolling elements allow for immediate, effortless re-lubrication and inspection, ensuring optimal maintenance and prolonged operational stability in high-frequency applications.

R2-5 Open Inch Series Miniature Ball Bearing | Ultra-Low Friction & High-Speed Dynamics | 3.175×7.938×2.779mm

Comprehensive Applications

Perfectly suited for electromechanical engineers and precision equipment designers who require frictionless rotation within sealed housings:

Precision Motors & Drives
  • Enclosed Stepper and Servo Motors
  • High-Speed Micro Spindles
  • Compact Gearbox Assemblies
  • Precision Actuator Mechanisms
Optical & Scientific Instrumentation
  • Telescope Mounts and Tracking Systems
  • Internal Rotary Encoders
  • Spectrometer Moving Parts
  • Sealed Laboratory Measurement Devices
Aerospace & Defense Micro-Mechanics
  • Internal Gyroscope Gimbals
  • Avionics Instrumentation Panels
  • Miniature Guidance Systems
  • Enclosed Target Tracking Actuators
Specialty Electronics
  • High-End Audio Equipment Mechanisms
  • Precision Tape and Film Guides
  • Internal Computer Hard Drive Components
  • Sealed Cooling Fan Rotors

Key Performance Features

01. Open Architecture for Zero Friction

Designed without seals or shields, the internal balls and cage are fully exposed. This unshielded construction completely removes the mechanical drag associated with seal-lip contact or shield proximity, resulting in an exceptionally low starting and running torque. It also allows for superior oil circulation and thermal dissipation in submerged or mist-lubricated environments.

02. Premium SAE 52100 Chrome Steel

Forged from industrial-grade GCr15 Chrome Steel, the raceways and ball bearings undergo rigorous thermal processing to ensure high structural rigidity and surface hardness. This robust metallurgical profile prevents premature wear, deformation, and surface fatigue, maintaining stringent ISO 492 precision tolerances over millions of rotational cycles.

03. Space-Optimized Inch Dimensions

Offering a fractional footprint, the 1/8-inch bore and 5/16-inch outer diameter provide an industry-standard fit for inch-based micro-assemblies. The open configuration boasts a slim 7/64-inch width, making it incredibly lightweight and perfectly suited for compact payload-sensitive applications where weight reduction is a priority.

Technical Specifications

Bearing Type Miniature Deep Groove Ball Bearing
ISO Dimension Series Inch Miniature Series
Basic Designation R2-5
Suffix Options Open (No Shields or Seals)
Bore Diameter (d) 1/8" (3.175 mm)
Outer Diameter (D) 5/16" (7.938 mm)
Width (B) 7/64" (2.779 mm)
Material (Races & Balls) Chrome Steel (GCr15 / SAE 52100) or Stainless Steel (AISI 440C)
Precision Class Standard / P5 Grade Available
Cage Material Pressed Steel (ribbon type) or Polyamide
Dynamic Load Rating (Cʳ) Approx. 544 N
Static Load Rating (C₀ʳ) Approx. 222 N
Limiting Speed (Grease) 50,000 RPM
Limiting Speed (Oil) 60,000 RPM
Weight (approx.) 0.65 grams

Interchange Part Numbers

Cross-reference equivalent part numbers for quick BOM integration and sourcing:

  • NMB: R2-5
  • SKF: R2-5
  • NSK: R2-5
  • NTN: R2-5
  • KOYO: R2-5

Design & Configuration

With 15 years of deep expertise in B2B manufacturing and international trade, Welink Bearing provides precision-engineered components tailored for industrial success. The R2-5 Open is a testament to our dedication to low-torque, high-speed rotational solutions. For OEM partners and large-scale manufacturing facilities, we accommodate custom production requests, including the application of specialized low-viscosity instrument oils, proprietary anti-rust treatments, and specific internal clearance ratings (such as C3 or CM) to precisely match your operational parameters.

"Unlock the potential of your high-speed enclosed mechanisms with the R2-5 Open inch series bearing—delivering uncompromising rotational freedom.”

Download Product Catalog (PDF)

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The R2-5 Open is a precision-engineered, inch-dimensional miniature deep groove ball bearing developed specifically for applications demanding absolute minimum rotational resistance. With a standard 1/8" bore diameter, this bearing utilizes an entirely unshielded (open) architecture. By eliminating the physical barriers of shields or rubber seals, the R2-5 Open achieves a zero-contact environment that eradicates frictional drag. This design is highly favored for mechanisms housed within clean, enclosed environments or oil-bath systems, where maximum RPM and rapid heat dissipation are critical for system performance.

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If you are interested in our products and want to know more details,please leave a message here,we will reply you as soon as we can.
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