1 Complete Model & Code Explanation

Model: W 638/5 R-2Z

Code Definition

W：Stainless steel series identifier

638/5：Basic dimension of miniature deep groove ball bearing

R：Enlarged ball reinforced load structure

2Z：Double non-contact metal shields

Structure：Double metal shields, no rubber contact seals

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

Important reminder: W 638/5 R-2Z is stainless steel miniature bearing with enlarged balls and double metal shields, suitable for radial loads and moderate bidirectional axial loads. R design adopts larger balls to achieve higher load capacity than standard 628/5 bearings with similar outline. 2Z metal shields only block dry solid dust. They do NOT resist water, mist, oil mist or liquid penetration and shall not be used under high humidity or splash conditions. Pre-greased for life at factory; shield construction is sealed and prohibits re-lubrication. Rotational resistance increases slightly and limiting speed decreases compared with open-type bearings.

Basic Parameters

Bore d：5 mm

Outer diameter D：13 mm

Width B：5 mm

Bearing type：Single-row deep groove ball bearing

Number of rows：Single row

Bore form：Straight cylindrical bore

Seal arrangement：2Z, double non-contact metal shields

Structural feature：R enlarged ball reinforced version

Oil groove：Without oil groove

Outer ring locating feature：No locating groove or shoulder

Cage：Stamped stainless steel cage

Radial internal clearance：CN standard clearance

Material：Stainless steel

Surface coating：Uncoated

Pre-installed lubricant：Long-life grease pre-filled at factory

Relubrication capability：On-site re-greasing unavailable

Duplex arrangement：Not supported, single unit operation only

Basic dynamic load rating：0.095 kN

Basic static load rating：0.046 kN

Reference speed：72 000 r/min

Limiting speed：47 000 r/min

Net weight：0.00019 kg

Indicative carbon footprint：0.00056 kg CO₂e

eClass code：23-05-08-01

UNSPSC code：31171504

Series Suffix Comparison

W 638/5 R：Open type, maximum rotational speed, no dust protection

W 638/5 R-Z：Single metal shield, one-side dust barrier

W 638/5 R-2Z：Double metal shields (this model), dual-side dust protection, enhanced load with enlarged balls

W 638/5 R-2RS1：Double rubber contact seals, dust & moisture resistant, lower limiting speed

638/5 R-2Z (without W)：Bearing steel variant, similar load capacity, no anti-corrosion property

2 Structure & Operating Characteristics

Japan NMT W 638/5 R-2Z is W-series stainless steel miniature deep groove ball bearing with enlarged ball structure and double non-contact metal shields. Developed for miniature precision transmissions requiring higher load capacity under dry dusty conditions. Fully stainless steel construction delivers basic corrosion resistance, suitable for dry equipment housings with mild condensation.

Adopts integrated stamped stainless steel cage to steadily retain enlarged balls and suppress vibration and noise at high speed. The R enlarged ball structure provides larger contact area than standard miniature bearings of identical size, boosting radial load capacity and adapting to continuous load applications. Tiny clearance exists between non-contact 2Z shields and rings, bringing limited friction increase to balance dust protection and high-speed performance. Dry airborne dust can be blocked, but water vapor and oil mist may penetrate through gaps. Long-life grease is permanently sealed inside upon production; shields cannot be removed for cleaning or re-lubrication. Standard CN radial clearance matches assembly tolerances of most miniature shafts.

The bearing mainly withstands radial loads and tolerates moderate bidirectional axial loads. Continuous exposure to water mist, liquid splash or heavy oil contamination is forbidden; media penetration will degrade grease and trigger corrosion and wear on raceways.

3 Core Performance Advantages

1. Miniature dimension 5×13×5 mm, R enlarged ball design provides higher load capacity than conventional 628/5 series under identical outer size.

2. W-series stainless steel substrate with basic rust resistance for clean environments with mild condensation.

3. Double 2Z non-contact metal shields blocking dry dust, lower friction loss than rubber sealed variants.

4. Factory pre-filled long-life grease for maintenance-free operation under standard working conditions.

5. Stamped stainless steel cage with lightweight rigid structure for long-duration continuous high-speed running of miniature bearings.

6. CN standard radial clearance delivers good interchangeability for direct replacement of same-size bearings.**

7. Reinforced load design, ideal for transmission points with constant load in small motors and portable tools.

4 Typical Application Fields

4.1 Precision Small Drive Motors

Miniature fan motors, spindles of beauty portable devices, built-in instrument drive motors.

4.2 Handheld Portable Power Tools

Compact grinding modules, miniature high-speed spindles, portable precision actuators.

4.3 Miniature Automation Fixture Components

Shafts of small encoders, automated test jigs, driven wheels of miniature linear mechanisms.

4.4 Intelligent & Model Equipment

Transmission parts of consumer smart appliances, small spindles for model aircraft, rotary components of portable sensors.

5 Assembly Specifications & Usage Guidelines

5.1 Assembly Environment & Operation Standards

Assemble in clean surroundings to avoid hard particles adhering to bearing surfaces. Never strike bearing end faces or shield areas directly. Apply uniform pressing force with proper sleeves to prevent shield denting or detachment. Strictly control interference fit between shaft and housing. Excessive interference reduces internal clearance, raises operating temperature at high speed and shortens grease service life. Store bearings without extrusion or impact to keep shields intact.

5.2 Selection Guidance

Fully sealed dust-free housing, maximum speed priority & light load → W 638/5 R open type

Dry atmosphere with floating dust, basic dust protection & steady load required → W 638/5 R-2Z (this model)

Dust risk on single side and limited installation space → W 638/5 R-Z single shield variant

Exposed to moisture and oil mist requiring moisture & oil resistance → W 638/5 R-2RS1 rubber sealed version

Dry indoor condition without anti-rust demand, cost optimization → 638/5 R-2Z bearing steel version

5.3 Lubrication Instruction

Special long-life grease is hermetically pre-filled inside the bearing for long service without maintenance under normal conditions. Shields are crimped and non-detachable, on-site re-greasing is impossible. Prolonged high temperature and continuous overspeed operation accelerate grease aging and shorten service life. Do not soak bearings in solvents; solvents will dissolve built-in lubricant and cause immediate failure.

5.4 Environmental Application Notes

2Z metal shields only defend dry dust, they cannot resist water, mist, liquid or oil vapor ingress. Choose 2RS1 rubber sealed type for high humidity, mist or oily environments. Stainless steel only provides basic rust resistance; oxidation corrosion will still occur under prolonged humid and waterlogged conditions.

6 Daily Maintenance & Fault Troubleshooting

Carry out short low-speed running-in after assembly; increase to rated speed only after confirming no abnormal noise and excessive temperature rise. Typical faults of 2Z sealed enlarged-ball miniature bearings: gradually rising noise, sluggish rotation, persistent overheating.

Common failure causes: grease deterioration due to moisture/oil mist intrusion, continuous overspeed operation, insufficient clearance from improper mounting, prolonged excessive axial load, foreign particle ingress leading to ball and raceway wear. Damaged raceways or worn balls cannot be repaired; replacement with new bearing is recommended upon failure.