W634-ZZ bearing: complete specifications & equivalents
The W634-ZZ is a ISO 15 radial bearing sized 4 x 16 x 5 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 | 4 mm |
| Outer diameter D | 16 mm |
| Width B | 5 mm |
| Material | SS440C |
| Seal / shield | ZZ |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 0.761 kN |
| Basic static load rating C0 | 0.265 kN |
| Fatigue load limit Pu | 0.011 kN |
| Reference speed (thermal) | 100000 rpm |
| Limiting speed (mechanical) | 50000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 5.15 g |
| Manufacturer designation | W 634-2Z |
| 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 | 0.157 in |
|---|---|
| Outer diameter D | 0.63 in |
| Width B | 0.197 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 6 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) | 3 of 40 |
| Bore above smallest 6300-series size | 2 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| W634-2RS | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 4×16×5 mm envelope and equivalent catalogue ratings; W 634-2RS1 is the two contact elastomer seals execution of this size — boundary dimensions interchangeable, only the seal/shield/cage execution differs. |
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 W634-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 final digit is the bore in millimetres: 634 fits a 4 mm shaft (direct-number miniature spelling). Envelope 4×16×5 mm (0.157×0.63×0.197 in), C 0.761 kN, C0 0.265 kN, Pu 0.011 kN; limiting speed 50000 r/min and mass 5.15 g. SKF spells the double shield W 634-2Z (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
- appliances exposed to moisture
- food and beverage conveyors
- pharmaceutical and packaging machines
- washdown-duty 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
- Corrosion resistance depends on clean, undamaged surfaces: never weld near W634-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 W634-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 — W634-ZZ is not marine-grade stainless.
- The stainless steel is martensitic and MAGNETIC; do not reject W634-ZZ over magnetism — only austenitic grades are non-magnetic, and those are too soft for bearing raceways.
- Clearance suffixes follow the seal code in the designation stack (e.g. W 634-2Z/C3 in SKF spelling); no suffix means normal CN internal clearance.
- Assign interference to the rotating ring: on a conventional shaft-mounted 4 mm position the inner ring rotates, so use a k5/m6 shaft seat with an H7 housing — reverse the logic if the outer ring rotates.
Frequently asked questions
What are the dimensions of the stainless W634-ZZ?
SKF W 634-2Z measures 4×16×5 mm (0.157×0.63×0.197 in), about 5.15 g, C 0.761 kN.
What does the W in W 634-2Z 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.
Are W stainless bearings waterproof?
No — the stainless rings resist moisture and weak chemicals far better than 52100 chrome steel, but salt spray, strong chlorides and unlubricated washdown duty can still corrode W634-ZZ; add seals and food-grade grease for wet positions.
Can I replace a chrome-steel bearing with stainless W634-ZZ?
The envelope matches, but stainless rates lower (C 0.761 kN for W 634-2Z); for corrosive environments that trade-off is intended, for high loads it shortens life.
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.