6308 Bearing Dimensions
6308 is a deep groove ball bearing with a 40 mm bore, 90 mm outer diameter and 23 mm width (40×90×23 mm, ISO 15). Open, ZZ, 2RS variants, designation breakdown, size-equivalent codes. Quote.
6308 specifications
| Bore d | 40 mm |
|---|---|
| Outside diameter D | 90 mm |
| Width B | 23 mm |
| Seal / shield options | Open; ZZ (two metal shields); 2RS (two rubber seals) |
| Material | GCr15 chrome bearing steel (rings and rolling elements) |
| Precision | P0 (standard); P6 on request |
| Vibration grade | Z3V3 (standard); other grades on request |
| Radial clearance | C0 (standard); C3 on request |
Load ratings & speed
| Dynamic load rating Cr | 36.45 kN |
|---|---|
| Static load rating C0r | 23.04 kN |
| Limiting speed, grease | 7,400 rpm |
| Limiting speed, oil | 8,700 rpm |
| Weight | 0.636 kg — approx. |
Values from FULI's catalog; confirm for your application.
Nearby 6300 series sizes: 6306 bearing · 6307 bearing · 6309 bearing · 6310 bearing
Grease quantity for 6308: bearing grease fill calculator.
Buying 6308 in quantity? See bearing wholesale supplier for pricing by quantity and shipping, and bearing manufacturer in China for how to check the factory.
How to read the 6308 designation
| Segment | Meaning |
|---|---|
| 6 | Single row deep groove ball bearing |
| 3 | Dimension series 03 (medium) |
| 08 | Bore code 08 → 40 mm bore. ISO bore code (00–03 = 10/12/15/17 mm; 04 and above = code × 5 mm). |
6308 cross reference by brand
The basic number 6308 means the same boundary dimensions at every maker listed here (40 × 90 × 23 mm). The suffix for shields, seals and clearance is written differently by each maker.
| Version | FULI | SKF | Timken | NSK | NTN | Koyo | NACHI |
|---|---|---|---|---|---|---|---|
| Open | 6308 | 6308 | 6308 | 6308 | 6308 | 6308 | 6308 |
| Shields both sides | 6308ZZ | 6308-2Z | 6308-ZZ | 6308ZZ | 6308ZZ | 6308 ZZ | 6308ZZE |
| Contact seals both sides | 6308-2RS | 6308-2RS1 | 6308-2RS | 6308DDU | 6308LLU | 6308 2RS | 6308-2NSE |
| Contact seals + C3 | 6308-2RS C3 | 6308-2RS1/C3 | 6308-2RS-C3 | — | — | — | — |
— = ask us. FULI radial clearance is C0 as standard and C3 on request.
SKF cross reference · Timken and Fafnir cross reference · NSK, NTN, Koyo and NACHI cross reference · Suffix meanings
Brand names are trademarks of their respective owners. FULI is not affiliated with, authorized by or endorsed by these companies. Part numbers are shown for interchange reference only. FULI dimensions, load ratings and speeds come from the FULI catalog.
Tolerances and fits for 6308
FULI makes 6308 to P0 as standard, with P6 on request. P0 is the Normal tolerance class of ISO 492; P6 limits are tighter. These are the P0 limits for the 40 × 90 × 23 mm size.
| Dimension | Nominal, mm | Deviation, µm | Limits, mm |
|---|---|---|---|
| Bore d (Δdmp) | 40 | 0 / −12 | 40.000 / 39.988 |
| Outside diameter D (ΔDmp) | 90 | 0 / −15 | 90.000 / 89.985 |
| Width B (ΔBs) | 23 | 0 / −120 | 23.000 / 22.880 |
Δdmp and ΔDmp: deviation of the mean bore and mean outside diameter in one radial plane. ΔBs: inner ring width; the outer ring width has the same limits.
Shaft and housing fits (general guidance)
For an inner ring that turns with a solid steel shaft under normal load, bearing makers’ fit tables give 40 k5 for the shaft of 6308. The housing bore is usually H7, or J7 where the outer ring must not creep.
| Seat | Deviation, µm | Limits, mm | Fit with 6308 |
|---|---|---|---|
| Shaft 40 k5 | +13 / +2 | 40.013 / 40.002 | 2 to 25 µm interference |
| Housing 90 H7 | +35 / 0 | 90.035 / 90.000 | 0 to 50 µm clearance |
| Housing 90 J7 | +22 / −13 | 90.022 / 89.987 | 13 µm interference to 37 µm clearance |
Taking the loosest and the tightest combination of limits, a P0 6308 on a 40 mm k5 shaft has 2 to 25 µm interference. Its outer ring has 0 to 50 µm clearance in an H7 bore and 13 µm interference to 37 µm clearance in a J7 bore.
This is general guidance, not a FULI specification. Heavy or shock loads, a hollow shaft, a thin-walled, split or light-alloy housing, or a large temperature difference between shaft and housing call for other classes, and the drawing of your machine takes priority. A tight shaft fit or a hot housing uses up internal clearance, and that is when C3 is chosen instead of C0.
If the outer ring turns and the shaft stands still, as in an idler pulley or a wheel hub, the fits are reversed: the housing gets the interference fit (for example N7 or P7) and the shaft a sliding one (g6 or h6).
Sources: ISO 492 tables as printed in the NTN catalogue CAT. No. 2203/E (Tables 6.4 and 6.5) and the RKB tolerance catalogue; ISO 286-2 for the seats; SKF and NTN fit tables for the shaft and housing classes.
6308 compared with nearby sizes
6308 measures 40 × 90 × 23 mm: bore d, outside diameter D and width B. Other deep groove ball bearings on this site for the same 40 mm shaft are 6808 (40 × 52 × 7 mm), 6908 (40 × 62 × 12 mm), 16008 (40 × 68 × 9 mm), 6008 (40 × 68 × 15 mm), 6208 (40 × 80 × 18 mm) and 6408 (40 × 110 × 27 mm).
6408 is the next heavier choice for a 40 mm shaft, with an outside diameter 20 mm larger (110 mm) and 4 mm more width (27 mm). In FULI's catalog 6408 has a dynamic load rating of 63.50 kN against 36.45 kN and a weight of about 1.230 kg against 0.636 kg for 6308.
6208 is the lighter option on the same shaft, with an outside diameter 10 mm smaller (80 mm) and 5 mm less width (18 mm), for housings with less room. In FULI's catalog 6208 has a dynamic load rating of 26.19 kN against 36.45 kN and a weight of about 0.366 kg against 0.636 kg for 6308.
6210 has the same 90 mm outside diameter with a 50 mm bore, so it fits the same housing bore on a larger shaft.
6406 has the same 90 mm outside diameter with a 30 mm bore, so it fits the same housing bore on a smaller shaft.
In the 63 (medium) series the sizes either side of 6308 are 6307 for a 35 mm shaft and 6309 for a 45 mm shaft.
| Model | Compared with this page | d × D × B (mm) | Cr (kN) | Weight (kg) |
|---|---|---|---|---|
| 6308 | This page | 40 × 90 × 23 | 36.45 | 0.636 |
| 6307 | Next size down | 35 × 80 × 21 | 30.15 | 0.464 |
| 6309 | Next size up | 45 × 100 × 25 | 47.70 | 0.829 |
| 6808 | Same bore | 40 × 52 × 7 | 4.59 | 0.031 |
| 6908 | Same bore | 40 × 62 × 12 | 13.14 | 0.112 |
| 16008 | Same bore | 40 × 68 × 9 | 11.34 | 0.130 |
| 6008 | Same bore | 40 × 68 × 15 | 15.12 | 0.190 |
| 6208 | Same bore | 40 × 80 × 18 | 26.19 | 0.366 |
| 6408 | Same bore | 40 × 110 × 27 | 63.50 | 1.230 |
| 6210 | Same outside diameter | 50 × 90 × 20 | 31.50 | 0.459 |
| 6406 | Same outside diameter | 30 × 90 × 23 | 43.50 | 0.735 |
Cr and weight from FULI's catalog; — = not listed on this site.
6308 weight, load ratings and speed
FULI's catalog gives the weight of 6308 as about 0.636 kg, so 100 bearings weigh about 63.6 kg and 1,000 about 636 kg before packing. The open, ZZ and 2RS versions share this catalog line.
6308 has a dynamic load rating Cr of 36.45 kN and a static load rating C0r of 23.04 kN. Cr is the load used to work out rating life; C0r is the reference for loads carried while the bearing is stationary or turning slowly. Limiting speeds in the catalog are 7,400 rpm with grease and 8,700 rpm with oil.
Contact seals add friction at the lip, so 6308-2RS usually runs below the speed of the open bearing. Ask us for the limit of the version you order.
Values from FULI's catalog; confirm for your application.
6308 versions: open, ZZ, 2RS and C3
Every version of 6308 has the same 40 × 90 × 23 mm boundary dimensions; only the cover between the rings and the internal clearance change. FULI supplies open, ZZ and 2RS versions, with C0 clearance as standard and C3 on request. Other makers write the same covers as 2Z or ZZ for shields and 2RS1, DDU or LLU for contact seals.
| Designation | What it is | Typical choice |
|---|---|---|
| 6308 | Open, no shields or seals | Housings with their own oil or grease supply |
| 6308-ZZ | Two metal shields, non-contact, greased | Motors and fans where dust is light |
| 6308-2RS | Two rubber contact seals, greased | Pumps, farm machinery and other wet or dusty places |
| 6308-ZZ C3 | ZZ with the larger C3 radial clearance | Tight shaft fit or a housing that runs hot |
| 6308-2RS C3 | 2RS with C3 radial clearance | Sealed bearings on a tight fit or running hot |
6308 dimensions in inches
The nearest common inch shaft size to the 40 mm bore of 6308 is 1-9/16 in (39.69 mm), 0.31 mm smaller than the bore, so 6308 would be loose on it. Inch shafts need an inch bearing, not a metric one with a sleeve or shim.
| Dimension | Millimetres | Inches |
|---|---|---|
| Bore d | 40 mm | 1.5748 in |
| Outside diameter D | 90 mm | 3.5433 in |
| Width B | 23 mm | 0.9055 in |
Converted at 1 in = 25.4 mm and rounded to four decimals. The bearing itself is made to the millimetre sizes.
Grease for 6308
FULI fills sealed 6308-2RS and 6308-ZZ bearings to about 30% of the free internal space as standard. The fill is set on an automatic greasing machine after sample sets are weighed before and after greasing. In normal use, sealed bearings usually do not need regreasing. A different fill level, a low-noise grease or a grease for a stated temperature range can be written on the order; for North America a range of −40 to 120 °C is often asked for.
Relubricating 6308 from the side takes about 10.3 g each time by the formula in our grease calculator: 0.005 × D × B = 0.005 × 90 × 23. This applies to the open 6308 in a housing with a grease supply.
How FULI supplies 6308
The standard 6308 from FULI has GCr15 chrome steel rings and balls, P0 precision, C0 radial clearance and vibration grade Z3V3; P6, C3 and other vibration grades are made on request. Radial clearance is set on automatic assembly equipment and sampled during production. Orders with a noise or vibration requirement are tested set by set before packing.
Rings are marked with a brand you are authorised to use, with the FULI brand, or left neutral, as your order states. The box is printed with the model, precision class and brand.
Inquiries that leave out the prefix or suffix letters are the usual cause of a wrong quote, so write the full designation, for example 6308-2RS C3.
Tools and guides for 6308
- Bearing size finder: look up a size from bore, OD and width
- Bearing weight chart
- Bearing grease fill calculator
- Shaft and housing tolerance chart
- Open, ZZ or 2RS seal selector
- Bearing internal clearance: C0, C3 and when to change
- Bearing lubrication basics
- Noise grade and precision class
- Ball bearing vs roller bearing
- All bearing products and model pages
Typical applications
- Electric motors
- Fans and blowers
- Water pumps
- Gearboxes
- Agricultural and textile machinery
FAQ
What is the difference between 6308 and 6408?
Both fit a 40 mm shaft. 6308 is 40 × 90 × 23 mm and 6408 is 40 × 110 × 27 mm, so 6408 has an outside diameter 20 mm larger (110 mm) and 4 mm more width (27 mm). In FULI's catalog 6408 has a dynamic load rating of 63.50 kN against 36.45 kN and a weight of about 1.230 kg against 0.636 kg for 6308. Choose 6408 for a higher load where the housing has room for it; 6308 keeps the housing smaller.
What is the difference between 6308 and 6208?
Both fit a 40 mm shaft. 6308 is 40 × 90 × 23 mm and 6208 is 40 × 80 × 18 mm, so 6208 has an outside diameter 10 mm smaller (80 mm) and 5 mm less width (18 mm). In FULI's catalog 6208 has a dynamic load rating of 26.19 kN against 36.45 kN and a weight of about 0.366 kg against 0.636 kg for 6308. 6208 suits a housing with less room; 6308 carries more load.
What size is 6308 in inches?
6308 is 1.5748 × 3.5433 × 0.9055 in (40 × 90 × 23 mm, d × D × B). The nearest common inch shaft size to the 40 mm bore of 6308 is 1-9/16 in (39.69 mm), 0.31 mm smaller than the bore, so 6308 would be loose on it. Use an inch bearing on an inch shaft.
How much does 6308 weigh?
About 0.636 kg in FULI's catalog, so 100 pieces weigh about 63.6 kg before packing. The open, ZZ and 2RS versions share this catalog line.
What is the difference between 6308-ZZ and 6308-2RS?
Both are 40 × 90 × 23 mm, the same as the open 6308. 6308-ZZ has two metal shields that do not touch the inner ring, so it runs with little drag but only keeps out coarse dirt. 6308-2RS has two rubber seals whose lips touch the inner ring; it keeps out water and fine dust at the cost of more friction. FULI fills both to about 30% of the free space.
How much grease does 6308 need?
Sealed 6308-2RS and 6308-ZZ come filled to about 30% of the free space and in normal use usually do not need regreasing. An open 6308 relubricated from the side takes about 10.3 g each time (0.005 × 90 × 23).
Is 6308 the same size across brands?
Yes. 6308 is an ISO designation, so the bore, outside diameter and width are the same whichever manufacturer made it. Brand-specific suffixes only change details such as seals, clearance or cage.