W639-3-ZZ bearing: complete specifications & equivalents
The W639-3-ZZ is a ISO 15 radial bearing sized 3 x 8 x 4 mm (bore x OD x width) with ZZ sealing. Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 3 mm |
| Outer diameter D | 8 mm |
| Width B | 4 mm |
| Material | SS440C |
| Seal / shield | ZZ |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 0.319 kN |
| Basic static load rating C0 | 0.09 kN |
| Fatigue load limit Pu | 0.004 kN |
| Reference speed (thermal) | 150000 rpm |
| Limiting speed (mechanical) | 75000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 0.82 g |
| Manufacturer designation | W 639/3-2Z |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-27
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & 6300-series range
| Bore d | 0.118 in |
|---|---|
| Outer diameter D | 0.315 in |
| Width B | 0.157 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 2.5 mm |
| Smallest bore in 6300-series | 2 mm |
| Largest outer diameter in 6300-series | 500 mm |
| Width range across 6300-series | 3–95 mm |
| Bore position in 6300-series (smallest first) | 2 of 40 |
| Bore above smallest 6300-series size | 1 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the W639-3-ZZ model number is decoded
The W prefix denotes SKF stainless steel deep-groove bearings (X108CrMo17 / AISI 440C class rings). In the 6300-series, the bore is written directly after the slash as 3 mm (bores below 10 mm use the slash spelling). Envelope 3×8×4 mm (0.118×0.315×0.157 in), C 0.319 kN, C0 0.09 kN, Pu 0.004 kN; limiting speed 75000 r/min and mass 0.82 g. SKF spells the double shield W 639/3-2Z (suffix 2Z); the shields are non-contact, retain grease and block coarse debris but are not liquid-tight. Stainless is chosen for corrosion and washdown duty, not for extra load — the same-envelope chrome-steel bearing rates higher.
Typical equipment & failure modes
Common applications
- washdown-duty equipment
- chemical and marine atmospheres
- medical and laboratory devices
- small pumps handling corrosive media
Known failure patterns
- seal and grease failure before the rings corrode in sustained washdown service
- surface staining and pitting when even the stainless steel is left unlubricated in salty or acidic duty
- fine-particle abrasion when non-contact shields let dust through in a dirty environment
- grease aging inside the shielded cavity with no relubrication path
Selection pitfalls — read before you substitute
- Food, pharmaceutical and washdown positions need food-grade grease (e.g. NSF H1 registered) inside W639-3-ZZ; standard fill is industrial grease unless specified otherwise.
- Corrosion resistance depends on clean, undamaged surfaces: never weld near W639-3-ZZ or scratch the raceways during mounting, since the damaged spot starts corrosion.
- Temperatures above roughly 300 °C temper the stainless races; even standard greases fail far earlier — keep W639-3-ZZ inside the quoted grease temperature range.
- W-prefix stainless rings (X108CrMo17 / AISI 440C class) resist moisture and weak chemicals but will still rust in chloride-rich or salt-spray duty without protection — W639-3-ZZ is not marine-grade stainless.
- Mount by heating the inner ring (max 120 °C) — driving W639-3-ZZ home through the outer ring or balls brinells the raceways.
- Do not preload W639-3-ZZ to silence it: a deep-groove ball bearing is not angular-contact, and axial preload only raises temperature and shortens grease life.
Frequently asked questions
What are the dimensions of the stainless W639-3-ZZ?
SKF W 639/3-2Z measures 3×8×4 mm (0.118×0.315×0.157 in), about 0.82 g, C 0.319 kN.
What does the W in W 639/3-2Z mean?
W is the SKF prefix for stainless steel deep-groove bearings (rings in X108CrMo17 / AISI 440C class); the rest of the designation follows the normal series and bore rules.
Where is W639-3-ZZ typically used?
Food and packaging machines, pharmaceutical equipment, washdown conveyors, chemical and marine-atmosphere drives and appliances exposed to moisture.
What grease is supplied in W639-3-ZZ?
Sealed units are pre-greased for life; for food or pharmaceutical duty order (or re-grease before service) with an NSF H1 registered food-grade grease.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-27. Read our editorial & correction policy.