W639-2-ZZ bearing: complete specifications & equivalents
The W639-2-ZZ is a ISO 15 radial bearing sized 2 x 6 x 3 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 | 2 mm |
| Outer diameter D | 6 mm |
| Width B | 3 mm |
| Material | SS440C |
| Seal / shield | ZZ |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 0.19 kN |
| Basic static load rating C0 | 0.051 kN |
| Fatigue load limit Pu | 0.002 kN |
| Reference speed (thermal) | 180000 rpm |
| Limiting speed (mechanical) | 90000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 0.31 g |
| Manufacturer designation | W 639/2-2Z |
| 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 | 0.079 in |
|---|---|
| Outer diameter D | 0.236 in |
| Width B | 0.118 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 2 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) | 1 of 40 |
| Bore above smallest 6300-series size | 0 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| W638-2-5-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 2×6×3 mm envelope as SKF W 638/2.5-2Z, but catalogue C/C0 differ (0.19/0.051 kN vs 0.117/0.036 kN) — envelope match only after a load check. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the W639-2-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 2 mm (bores below 10 mm use the slash spelling). Envelope 2×6×3 mm (0.079×0.236×0.118 in), C 0.19 kN, C0 0.051 kN, Pu 0.002 kN; limiting speed 90000 r/min and mass 0.31 g. SKF spells the double shield W 639/2-2Z (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
- chemical and marine atmospheres
- medical and laboratory devices
- small pumps handling corrosive media
- bicycle and outdoor equipment
Known failure patterns
- surface staining and pitting when even the stainless steel is left unlubricated in salty or acidic duty
- seal and grease failure before the rings corrode in sustained washdown service
- 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
- Stainless bearings carry lower load ratings than chrome steel of the same envelope: W639-2-ZZ is quoted at C 0.19 kN versus the 3 mm-wide 52100 version — do not swap on dimensions alone.
- Food, pharmaceutical and washdown positions need food-grade grease (e.g. NSF H1 registered) inside W639-2-ZZ; standard fill is industrial grease unless specified otherwise.
- Corrosion resistance depends on clean, undamaged surfaces: never weld near W639-2-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 W639-2-ZZ inside the quoted grease temperature range.
- Fillet radii must clear the W639-2-ZZ chamfer so the 3 mm-wide ring seats square; an oversized shaft radius creates point contact on the ring face.
- Fillet radii must clear the W639-2-ZZ chamfer so the 3 mm-wide ring seats square; an oversized shaft radius creates point contact on the ring face.
Frequently asked questions
What are the dimensions of the stainless W639-2-ZZ?
SKF W 639/2-2Z measures 2×6×3 mm (0.079×0.236×0.118 in), about 0.31 g, C 0.19 kN.
What does the W in W 639/2-2Z 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.
Is the stainless bearing magnetic?
Yes. Bearing stainless steels are martensitic (hardened) and magnetic; non-magnetic austenitic grades cannot be hardened enough for raceways and balls.
Where is W639-2-ZZ typically used?
Food and packaging machines, pharmaceutical equipment, washdown conveyors, chemical and marine-atmosphere drives and appliances exposed to moisture.
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.