1 Complete Model & Code Explanation

Model: W 618/2

Code Definition

W: Series symbol for stainless steel bearing

618: Extra-light thin-wall deep groove ball bearing series

/2: Dimension code corresponding to 2mm bore miniature specification

Open type without shields or rubber seals

Supply form: Single independent bearing, no factory duplex grinding, duplex DB/DF arrangement not recommended

Important reminder: W 618/2 is an extremely miniature stainless steel bearing with relatively low load capacity. It is designed primarily for radial loads and should not withstand large continuous axial forces. The open construction provides zero protection. Only use inside clean, dust-free enclosed housings; it cannot block dust or moisture ingress. No lubricant pre-filled at factory. A tiny amount of suitable lubricant should be applied during assembly. No relubrication path available, suitable for long-term maintenance-free, intermittent or short continuous high-speed operation.

Basic Parameters

Bore d: 2 mm

Outer diameter D: 5 mm

Width B: 1.5 mm

Bearing type: Single-row deep groove ball bearing

Number of rows: Single row

Bore form: Straight cylindrical bore

Seal arrangement: Open, no seal

Oil groove: Without oil groove

Outer ring locating feature: No locating groove or shoulder on outer ring

Cage: Stamped stainless steel cage

Radial internal clearance: CN standard clearance

Material: Stainless steel

Surface coating: Uncoated

Pre-installed lubricant: None

Relubrication capability: Not available

Duplex arrangement: Not supported, single unit operation only

Basic dynamic load rating: 0.074 kN

Basic static load rating: 0.021 kN

Reference speed: 220 000 r/min

Limiting speed: 140 000 r/min

Net weight: 0.00006 kg

Indicative carbon footprint: 0.00015 kg CO₂e

eClass code: 23-05-08-01

UNSPSC code: 31171504

Series Suffix Comparison

W 618/2: 2mm bore open stainless steel miniature bearing (this model)

W618/2-Z: Single metal shield, simple dust protection, slightly lower limiting speed

W618/2-2Z: Double metal shields, better dust resistance, higher frictional temperature rise

618/2: Bearing steel version with identical dimensions, similar load capacity, no rust resistance

2 Structure & Operating Characteristics

Japan NMT W 618/2 is a W618 thin-wall miniature stainless steel deep groove ball bearing, developed for ultra-compact rotary mechanisms with extreme space constraints. Manufactured entirely from stainless steel, it offers basic rust resistance compared with bearing steel miniature bearings, ideal for sealed precision equipment with minor internal humidity and infrequent maintenance access.

Equipped with one-piece stamped stainless steel cage. Compact and ultra-lightweight, delivering stable dynamic balance to reduce vibration risk at high rotational speeds. Standard CN radial clearance balances assembly convenience and smooth rotation, matching common tolerance requirements for miniature shafts. The open unsealed design eliminates friction from sealing elements to achieve extremely high limiting speed, making it a preferred high-speed solution for bearings of this size class.

Due to ultra-small overall dimensions, limited contact area between rolling elements and raceways results in low load capacity. The bearing is optimized for radial loads; only minimal axial preload is permitted. Continuous heavy axial thrust must be avoided. Without sealing protection, raceways are fully exposed. External dust and moisture easily cause corrosion and abrasive wear, therefore operation requires strictly clean internal environment.

3 Core Performance Advantages

1. Ultra-miniature outline: 2mm bore × 5mm OD × 1.5mm width, fits minimal installation envelope.

2. Stainless steel construction: Provides basic anti-corrosion property for slightly humid enclosed housings.

3. Open unsealed design: No sealing friction loss, enables ultra-high rotational speed.

4. Stamped stainless steel cage: Lightweight structure for stable high-speed performance.

5. CN standard radial clearance: High universality matching most miniature shaft tolerance standards.

6. Ultra-low net weight: Low rotational inertia, sensitive start-stop response.

4 Typical Application Fields

4.1 Micro Transmission Parts for Precision Medical Equipment

Rotary assemblies of minimally invasive detection probes, micro shafts inside portable diagnostic instruments, sealed clean internal mechanisms.

4.2 Adjustment Modules for Optical Instruments

Rotary fine-tuning shafts on microscopy equipment, miniature lens angle adjustment units, precision optical sensor rotary components.

4.3 Miniature Testing & Sensing Devices

Laboratory micro test fixtures, rotary structures for micro flow sensors, portable precision detection equipment.

4.4 Compact Precision Drive Components

Micro precision motors, built-in high-speed miniature rotary units inside small intelligent devices (dust-tight enclosed housings).

5 Assembly Specifications & Usage Guidelines

5.1 Assembly Environment & Operation Standards

Assembly of W 618/2 miniature precision bearing must be performed on a dust-free clean workstation to prevent dust and fiber contamination on raceways. Never strike the bearing directly. Use dedicated micro tooling for controlled press fitting to avoid ring tilting and rolling element damage. Take precautions against loss during handling due to tiny size. Strictly control fit tolerances of shaft and housing. Excessive interference will drastically reduce internal clearance and lead to overheating or seizure at high speed.

5.2 Selection Guidance

Extreme space limitation, maximum speed priority, clean sealed cavity → W 618/2 open type (this model);

Minor dry dust present, moderate speed requirement acceptable → W618/2-Z / 2Z shielded variant;

Dry environment without anti-rust requirement, higher load expected → 618/2 bearing steel version.

5.3 Lubrication Scheme

No lubricant pre-filled at factory. Apply a minimal quantity of low-viscosity high-speed grease or oil during assembly. Avoid over-lubrication; excess lubricant creates churning resistance and sharp temperature rise under high speed. Synthetic low-viscosity lubricants formulated for miniature bearings are recommended for continuous ultra-high speed operation. No built-in relubrication channel. Designed for maintenance-free service, not suitable for heavy continuous duty requiring periodic re-greasing.

5.4 Environmental Application Notes

This open bearing has zero dust or liquid protection capability. Never expose directly to atmospheric dust, moisture or cleaning fluid. Equipment must feature a fully sealed housing to isolate contaminants. Stainless steel offers basic rust resistance only; long-term operation in salt spray or chemical vapor atmosphere is prohibited.

6 Daily Maintenance & Fault Troubleshooting

Carry out low-speed short running-in after assembly. Gradually increase speed to operating level only after confirming no abnormal noise or temperature rise. Failure signs are difficult to observe on micro bearings. Stiff rotation or increased torque usually indicates contaminant ingress or surface corrosion on raceways.

Common failure causes: foreign dust entering rolling contact zone, insufficient or excessive lubricant, clearance loss caused by improper mounting, sustained axial overload. Once faults occur, replacement is recommended; repair is generally not feasible for miniature bearings.