638-8-ZZ bearing: complete specifications & equivalents
The 638-8-ZZ is a ISO 15 radial bearing sized 8 x 16 x 6 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 | 8 mm |
| Outer diameter D | 16 mm |
| Width B | 6 mm |
| Material | GCr15 |
| Seal / shield | ZZ |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 1.33 kN |
| Basic static load rating C0 | 0.57 kN |
| Fatigue load limit Pu | 0.024 kN |
| Reference speed (thermal) | 90000 rpm |
| Limiting speed (mechanical) | 45000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 4.3 g |
| Manufacturer designation | 638/8-2Z |
| 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 & 63800-series range
| Bore d | 0.315 in |
|---|---|
| Outer diameter D | 0.63 in |
| Width B | 0.236 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 4 mm |
| Smallest bore in 63800-series | 1.5 mm |
| Largest outer diameter in 63800-series | 28 mm |
| Width range across 63800-series | 2–9 mm |
| Bore position in 63800-series (smallest first) | 7 of 8 |
| Bore above smallest 63800-series size | 6.5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| W638-8-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 8×16×6 mm envelope, but the stainless and chrome-steel executions carry different catalogue ratings (1.33/0.57 kN vs 0.715/0.3 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 638-8-ZZ model number is decoded
In the miniature 63800-series, the bore is written directly after the slash as 8 mm (bores below 10 mm use the slash spelling). The envelope is 8×16×6 mm (0.315×0.63×0.236 in) with a 4.0 mm radial section height, C 1.33 kN, C0 0.57 kN and Pu 0.024 kN. SKF spells the double shield 638/8-2Z (suffix 2Z); the shields are non-contact, retain grease and block coarse debris but are not liquid-tight. Limiting speed 45000 r/min, catalogue mass 4.3 g. A thin section saves space but leaves little margin for misalignment or shaft deflection.
Typical equipment & failure modes
Common applications
- small fans and blowers
- hand-held power tools
- domestic appliances
- instrument and encoder drives
Known failure patterns
- fine-particle abrasion when non-contact shields let dust through in a dirty environment
- grease aging inside the shielded cavity with no relubrication path
- edge loading from shaft deflection or housing misalignment
- rolling-contact fatigue spalling once the catalogue L10 life is exceeded
Selection pitfalls — read before you substitute
- Clearance suffixes follow the seal code in the designation stack (e.g. 638/8-2Z/C3 in SKF spelling); no suffix means normal CN internal clearance.
- Fillet radii must clear the 638-8-ZZ chamfer so the 6 mm-wide ring seats square; an oversized shaft radius creates point contact on the ring face.
- Shields on 638-8-ZZ are non-contact: chips and coarse dust stay out, but water passes straight through — specify the sealed 638/8-2RS for washdown duty.
- Do not pry the caps off 638-8-ZZ to repack it; shield/seal damage leaves a gap that throws grease and admits dirt.
- 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 638-8-ZZ (C 1.33 kN, C0 0.57 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 638-8-ZZ?
The SKF 638/8-2Z measures 8 mm bore × 16 mm OD × 6 mm width (0.315 × 0.63 × 0.236 in), mass about 4.3 g. It has two non-contact sheet-metal shields.
Why is there a slash in the designation 638/8-2Z?
The slash writes a bore that falls outside the two-digit code table: 638/8 means 8 mm bore. The site slug 638-8-ZZ replaces the slash with a hyphen.
What is the difference between 638-8-ZZ and a same-bore 62-series bearing?
Section height differs: 638-8-ZZ has a 4 mm radial section and C 1.33 kN; always match d, D and B — same bore alone never makes two bearings interchangeable.
Which fits should I use for 638-8-ZZ?
With a rotating inner ring use roughly j5/k5 on the shaft and H7 in the 16 mm housing; reverse the interference if the outer ring rotates.
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.