W618-8 bearing: complete specifications & equivalents
The W618-8 is a ISO 15 radial bearing sized 8 x 16 x 4 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 8 mm |
| Outer diameter D | 16 mm |
| Width B | 4 mm |
| Material | SS440C |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 0.715 kN |
| Basic static load rating C0 | 0.3 kN |
| Fatigue load limit Pu | 0.012 kN |
| Reference speed (thermal) | 90000 rpm |
| Limiting speed (mechanical) | 56000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 3.1 g |
| Manufacturer designation | W 618/8 |
| 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 & 61800-series range
| Bore d | 0.315 in |
|---|---|
| Outer diameter D | 0.63 in |
| Width B | 0.157 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 4 mm |
| Smallest bore in 61800-series | 1 mm |
| Largest outer diameter in 61800-series | 1820 mm |
| Width range across 61800-series | 1–140 mm |
| Bore position in 61800-series (smallest first) | 9 of 74 |
| Bore above smallest 61800-series size | 7 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 618-8 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 8×16×4 mm envelope, but the stainless and chrome-steel executions carry different catalogue ratings (0.715/0.3 kN vs 0.819/0.3 kN) — envelope match, not a load-rating equivalent; choose by corrosion versus load duty. |
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 W618-8 model number is decoded
The W prefix denotes SKF stainless steel deep-groove bearings (X108CrMo17 / AISI 440C class rings). In the 61800-series, the bore is written directly after the slash as 8 mm (bores below 10 mm use the slash spelling). Envelope 8×16×4 mm (0.315×0.63×0.157 in), C 0.715 kN, C0 0.3 kN, Pu 0.012 kN; limiting speed 56000 r/min and mass 3.1 g. The open W 618/8 carries no shields or seals and relies on application lubrication and external sealing. 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
- contamination wear when the open arrangement is used without external seals
- lubricant starvation where no regreasing interval is maintained
Selection pitfalls — read before you substitute
- 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 — W618-8 is not marine-grade stainless.
- The stainless steel is martensitic and MAGNETIC; do not reject W618-8 over magnetism — only austenitic grades are non-magnetic, and those are too soft for bearing raceways.
- Stainless bearings carry lower load ratings than chrome steel of the same envelope: W618-8 is quoted at C 0.715 kN versus the 4 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 W618-8; standard fill is industrial grease unless specified otherwise.
- At 8 mm bore, C3 clearance is the safe choice when interference fits plus temperature rise consume the CN clearance; a hot tight bearing with no residual clearance fails fast.
- Catalogue ratings for W618-8 (C 0.715 kN, C0 0.3 kN) are SKF figures from PUB BU/P1 17000; geometry revisions can change ratings without changing the designation, so keep the catalogue edition with the specification.
Frequently asked questions
What are the dimensions of the stainless W618-8?
SKF W 618/8 measures 8×16×4 mm (0.315×0.63×0.157 in), about 3.1 g, C 0.715 kN.
What does the W in W 618/8 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 W618-8 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.