Product Overview

The NMT W 618/2 is an open, single-row miniature stainless steel deep groove ball bearing. With a 2 mm bore, 5 mm outer diameter, and 1.5 mm width , this bearing is one of the smallest standardized precision bearings in the bearing industry. Manufactured entirely from stainless steel (both rings and rolling elements) with a stamped stainless steel cage , it integrates extreme miniaturization, ultra-high speed, 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 0.094 kN  and a static load rating of 0.025 kN . It achieves a reference speed of 200,000 r/min  and a limiting speed of 120,000 r/min . The bearing weighs only 0.0001 kg (0.1 g)  with a carbon footprint of just 0.0004 kg CO₂e, making it the ultimate choice for extreme miniaturization and ultra-high-speed applications. The operating temperature range is -30°C to 110°C.

 

Model Code Decoding – Understanding NMT W 618/2

Code Meaning

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

618 Basic series designation, ultra-thin series deep groove ball bearing

/2 Bore size code, indicating 2 mm bore diameter

Core Value: The W-series stainless steel material provides excellent corrosion resistance and chemical resistance . The 618 ultra-thin series design delivers stable load capacity within an ultra-narrow 1.5 mm width. The stamped stainless steel 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 120,000 r/min limiting speed . This bearing features an open design with no seals  and a cylindrical bore . Shoulder diameters: d₁ ≈ 2.7 mm, D₁ ≈ 3.9 mm , chamfer dimension r₁,₂ min. 0.08 mm . The synergy of extreme miniaturization, ultra-high speed, and stainless steel corrosion resistance makes this bearing the ultimate bearing solution for miniature ultra-high-speed precision equipment.

 

Core Performance Advantages

1. Extreme Miniaturization – Only 2×5×1.5 mm

With an outer diameter of only 5 mm and a width of only 1.5 mm , weighing just 0.0001 kg (0.1 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 .

 

2. 120,000 r/min Ultra-High Speed – Industry-Leading Performance

This bearing achieves a reference speed of 200,000 r/min  and a limiting speed of 120,000 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 .

 

3. Stainless Steel Material – Corrosion Resistance, Extended Life

Manufactured entirely from stainless steel (AISI 440/9Cr18) , 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.

 

4. 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. The filling-slot-free design ensures stability and low noise operation at high speeds .

 

5. Ultra-Lightweight – Only 0.1 Grams

The bearing weighs only 0.0001 kg (0.1 g)  with a carbon footprint of just 0.0004 kg CO₂e. The extremely low rotating mass effectively reduces centrifugal loads and inertia moments at high speeds.

 

6. 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 .

 

7. Stamped Stainless Steel Cage – Speed and Durability Combined

The stamped stainless steel 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 120,000 r/min limiting speed.

 

8. Open Design – Flexible Lubrication Options

This bearing features an open design (unsealed) , allowing flexible selection of lubrication methods based on application – grease lubrication for general ultra-high-speed applications, oil-mist or oil-air lubrication for extreme ultra-high-speed machining.

 

9. Clear Performance Specifications

 

Parameter Value

Bore d 2 mm 

Outer Diameter D 5 mm 

Width B 1.5 mm 

Shoulder Diameter d₁ ≈ 2.7 mm 

Shoulder Diameter D₁ ≈ 3.9 mm 

Chamfer r₁,₂ min. 0.08 mm 

Dynamic Load Rating C 0.094 kN 

Static Load Rating C₀ 0.025 kN 

Fatigue Load Limit Pu 0.001 kN 

Reference Speed 200,000 r/min 

Limiting Speed 120,000 r/min 

Minimum Load Factor kr 0.02 

Calculation Factor f₀ 6.5 

Ball Material Stainless Steel (AISI 440) 

Ring Material Stainless Steel (AISI 440) 

Cage Material Stamped Stainless Steel 

Seal Type Open (Unsealed) 

Tolerance Class P0 (Normal) 

Radial Clearance CN (Normal) 

Weight 0.0001 kg (0.1 g) 

Temperature Range -30°C to 110°C

Typical Applications

The NMT W 618/2, with its 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, chromatography products 

 

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

 

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

 

Semiconductor Manufacturing Equipment – precision wafer processing, chip packaging

 

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

 

Textile Machinery – high-speed miniature transmission mechanisms 

 

Food Machinery – corrosion-resistant miniature transmission mechanisms

 

Aerospace Micro-Components – micro-actuators, sensors

 

Industrial Robots – micro high-speed rotary joints

 

Models and Toys – micro high-speed rotating components

 

Electromechanical Equipment and Aerial Work Platforms – miniature precision rotary units 

 

Important Installation Notes

✅ This bearing features an open design (unsealed)  – select appropriate lubrication method based on application: grease lubrication for general ultra-high-speed applications, oil-mist or oil-air lubrication for extreme ultra-high-speed machining (120,000 r/min) .

 

✅ This bearing is manufactured from stainless steel (AISI 440/9Cr18) , offering excellent corrosion resistance, particularly suitable for humid or corrosive environments.

 

✅ Ensure shaft and housing fits comply with P0 grade requirements (bore 2 mm, OD 5 mm) . Shaft abutment diameter: da min. 2.5 mm, da max. 2.6 mm; housing abutment diameter: Da max. 4.4 mm; maximum chamfer radius: ra max. 0.08 mm .

 

✅ Due to the extremely small size (only 0.1 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 seals – ensure lubrication method and maintenance intervals are properly matched.

 

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 618/2 bearing is manufactured to strict Japanese quality standards – from ring material (high-purity stainless steel AISI 440)  and rolling elements to superfinishing processes. The combination of stainless steel material (W series), 618 ultra-thin series design, stamped stainless steel 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 extreme miniaturization, ultra-high speed, and corrosion resistance.

 

Choose NMT W 618/2 for:

 

✅ Extreme miniaturization – 2×5×1.5 mm, only 0.1 g

 

✅ 120,000 r/min ultra-high-speed performance – industry-leading

 

✅ Stainless steel material – corrosion resistance, extended life

 

✅ Deep groove design – bidirectional load capacity, excellent versatility

 

✅ Stamped stainless steel cage – low friction, high speed

 

✅ Open design – flexible lubrication options

 

✅ Ultra-lightweight – carbon footprint only 0.0004 kg CO₂e

 

✅ Japanese precision manufacturing quality