Product Overview

The NMT W 638/2.5-2Z is a shielded, single-row miniature stainless steel deep groove ball bearing. With a 2.5 mm bore, 6 mm outer diameter, and 2.6 mm width, this bearing is manufactured entirely from stainless steel (both rings and rolling elements) with a stainless steel stamped cage, equipped with non-contact metal shields on both sides (2Z) and pre-filled with high-quality grease. It integrates extreme miniaturization, ultra-high speed, maintenance-free sealing, corrosion resistance, and super-precision rotational accuracy into a single package, accommodating radial and bidirectional axial loads simultaneously.

 

The bearing offers a basic dynamic load rating of 0.117 kN, a static load rating of 0.036 kN, and a fatigue load limit of 0.002 kN. It achieves a reference speed of 170,000 r/min and a limiting speed of 85,000 r/min. The bearing weighs only 0.0003 kg (0.3 g) with an operating temperature range of -30°C to 120°C.

 

Model Code Decoding – Understanding NMT W 638/2.5-2Z

Code Meaning

W Stainless steel material – rings and rolling elements made of corrosion-resistant stainless steel

638 Basic series designation, miniature deep groove ball bearing series

/2.5 Bore size code, indicating 2.5 mm bore diameter

-2Z Shield on both sides – non-contact metal shields on both sides

Core Value: The W-series stainless steel material provides excellent corrosion resistance and chemical resistance. The 638 miniature series design delivers stable load capacity within an ultra-narrow 2.6 mm width. The 2Z metal shields effectively prevent contaminant ingress while the non-contact design adds no extra resistance or heat generation. The bearing comes pre-lubricated from the factory and is maintenance-free – no washing or relubrication is required. The stainless steel stamped cage ensures reliable rolling element guidance at ultra-high speeds. The P0 normal precision class combined with CN radial internal clearance ensures low friction, low vibration, and low noise operation even at the 85,000 r/min limiting speed. This bearing features no lubrication groove and a cylindrical bore. The synergy of extreme miniaturization, ultra-high speed, maintenance-free sealing, and stainless steel corrosion resistance makes this bearing the ultimate bearing solution for miniature ultra-high-speed precision equipment.

 

Core Performance Advantages

1. Double Metal Shields – Maintenance-Free, Extended Life

The bearing features non-contact metal shields on both sides (2Z) that effectively prevent contaminants such as dust and debris from entering the bearing interior, while the non-contact design avoids friction between the shield and the inner ring – adding no extra resistance or heat generation. The bearing is pre-filled with high-quality grease at the factory and is maintenance-free – no washing or relubrication is required. This ensures stable temperature performance even at 85,000 r/min ultra-high speeds, while significantly extending maintenance intervals.

 

2. Extreme Miniaturization – Only 2.5×6×2.6 mm

With an outer diameter of only 6 mm and a width of only 2.6 mm, weighing just 0.0003 kg (0.3 g), this bearing is one of the smallest standardized precision bearings in the world. It is particularly suitable for applications with extreme space constraints, such as precision instruments, miniature motors, medical devices, and optical scanners.

 

3. 85,000 r/min Ultra-High Speed – Industry-Leading Performance

This bearing achieves a reference speed of 170,000 r/min and a limiting speed of 85,000 r/min. The low-friction design and optimized internal geometry ensure stable operation and low heat generation at extreme speeds. This speed level makes it the ideal choice for high-speed miniature motors, precision instrument spindles, dental handpieces, and other ultra-high-speed miniature devices.

 

4. Stainless Steel Material – Corrosion Resistance, Extended Life

Manufactured entirely from stainless steel, this bearing provides excellent corrosion resistance and chemical resistance. In humid, corrosive, or high-cleanliness environments, stainless steel bearings effectively resist rust and chemical attack, significantly extending service life. This makes them particularly suitable for medical devices, food machinery, optical instruments, semiconductor equipment, and other applications with strict cleanliness and corrosion resistance requirements.

 

5. Deep Groove Design – Bidirectional Load Capacity, Excellent Versatility

Deep groove ball bearings feature a simple structure, wide versatility, and low friction. This bearing can accommodate radial loads and bidirectional axial loads simultaneously, providing excellent load capacity in miniaturized designs.

 

6. Ultra-Lightweight – Only 0.3 Grams

The bearing weighs only 0.0003 kg (0.3 g). The extremely low rotating mass effectively reduces centrifugal loads and inertia moments at high speeds.

 

7. P0 Normal Precision + CN Radial Clearance – Versatility and Reliability Combined

This bearing features P0 normal precision class and CN normal radial internal clearance. This combination ensures reliable operation in the vast majority of general miniature applications, while facilitating easy installation and maintenance.

 

8. Stainless Steel Stamped Cage – Speed and Durability Combined

The stainless steel stamped cage provides reliable rolling element guidance and low friction at ultra-high speeds, contributing to reduced centrifugal forces, friction, and heat generation – a key factor in achieving the 85,000 r/min limiting speed.

 

9. Clear Performance Specifications

 

Parameter Value

Bore d 2.5 mm

Outer Diameter D 6 mm

Width B 2.6 mm

Shoulder Diameter d₁ ≈ 3.7 mm

Shoulder Diameter D₂ ≈ 5.4 mm

Chamfer r₁,₂ min. 0.08 mm

Dynamic Load Rating C 0.117 kN

Static Load Rating C₀ 0.036 kN

Fatigue Load Limit Pu 0.002 kN

Reference Speed 170,000 r/min

Limiting Speed 85,000 r/min

Minimum Load Factor kr 0.02

Calculation Factor f₀ 7.1

Ball Material Stainless Steel

Ring Material Stainless Steel

Cage Material Stainless Steel Stamped

Seal Type Double Metal Shields (2Z)

Tolerance Class P0 (Normal)

Radial Clearance CN (Normal)

Weight 0.0003 kg (0.3 g)

Temperature Range -30°C to 120°C

Typical Applications

The NMT W 638/2.5-2Z, with its shielded protection, extreme miniaturization, ultra-high speed, and stainless steel corrosion resistance, covers an exceptionally wide range of high-end miniature applications:

 

Precision Instruments – measuring devices, optical scanners, laser cutting equipment

 

Miniature Motors – high-speed micro-motors, stepper motors

 

Medical Devices – high-speed dental handpieces, surgical tools, safety protection equipment

 

Semiconductor Manufacturing Equipment – precision wafer processing, chip packaging

 

Optical Equipment – laser scanners, rotating mirrors, camera focusing mechanisms

 

Textile Machinery – textile industry accessories and components

 

Food Machinery – meat processing equipment, corrosion-resistant miniature transmission mechanisms

 

Aerospace Micro-Components – micro-actuators, sensors

 

Teaching Equipment – laboratory instruments, plant determination instruments

 

Industrial Robots – micro high-speed rotary joints

 

Logistics Equipment – automated logistics equipment

 

Important Installation Notes

✅ This bearing features double metal shields (2Z) and comes pre-filled with high-quality grease – maintenance-free. Ready to install out of the box – no washing or relubrication required.

 

✅ This bearing is manufactured from stainless steel, offering excellent corrosion resistance, particularly suitable for humid, corrosive, or high-cleanliness environments.

 

✅ Ensure shaft and housing fits comply with P0 grade requirements (bore 2.5 mm, OD 6 mm). Shaft abutment diameter: da min. 3.1 mm, da max. 3.6 mm; housing abutment diameter: Da max. 5.5 mm; maximum chamfer radius: ra max. 0.08 mm.

 

✅ Due to the extremely small size (only 0.3 g), use specialized miniature bearing installation tools and take extra care to avoid excessive force or impact.

 

✅ Installation in a clean environment is recommended to prevent contaminant ingress that could affect ultra-high-speed performance.

 

⚠️ This bearing has no preload setting – if paired configurations or specific preload are required, adjust based on application requirements.

 

⚠️ This bearing has no lubrication groove and no relubrication feature – the shielded design is lubricated for life, requiring no relubrication.

 

NMT Quality Commitment

Japan NMT (Enmutī) has deep expertise in the precision bearing industry, with breakthroughs in material purification, process refinement, scenario customization, and intelligent upgrading, transforming precision bearings into core solutions addressing pain points across multiple industries. The NMT W 638/2.5-2Z bearing is manufactured to strict Japanese quality standards – from ring material (high-purity stainless steel) and rolling elements to superfinishing processes. The combination of stainless steel material (W series), 638 miniature series design, double metal shields (2Z), stainless steel stamped cage, P0 precision class, and CN radial clearance makes this bearing the flagship precision bearing in the NMT miniature bearing series – offering the perfect balance of maintenance-free sealing, extreme miniaturization, ultra-high speed, and corrosion resistance.

 

Choose NMT W 638/2.5-2Z for:

 

✅ Double metal shields – maintenance-free, extended life

 

✅ Extreme miniaturization – 2.5×6×2.6 mm, only 0.3 g

 

✅ 85,000 r/min ultra-high-speed performance – industry-leading

 

✅ Stainless steel material – corrosion resistance, extended life

 

✅ Deep groove design – bidirectional load capacity, low friction, low noise

 

✅ Stainless steel stamped cage – low friction, high speed

 

✅ Factory pre-lubricated – ready to install

 

✅ Ultra-lightweight – only 0.3 g

 

✅ Japanese precision manufacturing quality