The SKF 6309-2Z/C3 is a single row deep groove ball bearing with a 45 mm bore, 100 mm outside diameter and 25 mm width, fitted with a non-contact metal shield on both sides (2Z) and C3 radial internal clearance. It belongs to the SKF Explorer performance class and, per SKF, carries a basic dynamic load rating of 55.3 kN and a basic static load rating of 31.5 kN.
The designation can be read directly: 6 = single row deep groove ball bearing, 3 = ISO dimension series 03 (medium), a heavier cross-section with larger balls for higher loads on the same shaft size; 09 = bore code for 45 mm (09 x 5); 2Z = shields on both sides; C3 = radial internal clearance greater than normal.
Shields leave a narrow gap to the inner ring, so friction stays low and SKF lists a limiting speed of 7,500 r/min for this version, compared with 4,500 r/min for the sealed 6309-2RS1/C3. That makes the 2Z design the usual choice for electric motors, fans and other clean, fast-running positions.
Technical data
| SKF designation | 6309-2Z/C3 |
|---|---|
| Bearing type | Single row deep groove ball bearing |
| Dimension series | 63 – ISO dimension series 03 (medium) |
| Bore diameter (d) | 45 mm |
| Outside diameter (D) | 100 mm |
| Width (B) | 25 mm |
| Basic dynamic load rating (C) | 55.3 kN |
| Basic static load rating (C0) | 31.5 kN |
| Reference speed | 15,000 r/min |
| Limiting speed | 7,500 r/min |
| SKF performance class | SKF Explorer |
| Sealing | Shield on both sides (non-contact) |
| Radial internal clearance | C3 (greater than normal) |
| Cage | Sheet metal (pressed steel) |
| Bore type | Cylindrical |
| Lubricant | Grease, no relubrication feature |
| Material | Bearing steel |
| Net weight | 0.85 kg |
| Condition | New, original SKF |
Typical applications
- Industrial gearboxes and drive trains
- Gearbox input shafts and speed reducers
- Fans, blowers and ventilation units
- Machine-tool and woodworking spindles running at moderate speed
- Like-for-like replacement of a worn SKF 6309-2Z/C3
Compatibility and replacement
Every 6309 bearing made to ISO 15 has the same 45 x 100 x 25 mm boundary dimensions, so this bearing fits wherever a 6309 with shields and C3 clearance from another maker was used. Suffixes differ between brands: shields are often marked ZZ or 2Z, contact seals 2RS, 2RS1, DDU or LLU, and the clearance C3 may appear as “C3” or “/C3”. Always match the sealing arrangement and the clearance class shown on the old bearing; if your machine needs the other closure, the 6309-2RS1/C3 is the same size.
Frequently asked questions
What is the difference between 6309-2Z/C3 and 6309-2RS1/C3?
Only the closures. The 6309-2Z has non-contact steel shields; the 2RS1 version has contact rubber seals. Per SKF, the limiting speed is 7,500 r/min for 2Z and 4,500 r/min for 2RS1; the load ratings are the same. Choose shields for speed and low friction, seals for dirt and moisture.
What do the load ratings mean in practice?
The basic dynamic load rating C (55.3 kN) is used to calculate rating life: under ISO 281, a ball bearing loaded at one tenth of C has a basic rating life of 1,000 million revolutions. The static rating C0 (31.5 kN) is the reference for heavy loads at very low speed or standstill.
What does C3 mean, and can I use a bearing without it?
C3 is a radial internal clearance greater than normal. It leaves room for the inner ring to expand with a tight shaft fit or with heat, which is why electric motors and hot-running machines often specify it. Fit the clearance class the machine maker specifies or that is marked on the old bearing; do not swap C3 for normal clearance without checking.
Related parts
- SKF 6309-2RS1/C3 (sealed version)
- SKF 6308-2Z/C3 (40 mm bore)
- SKF 6310-2Z/C3 (50 mm bore)
- All SKF 6300 Series Bearings
Part of the SKF 6300 series stocked by RendatSP for electric motors, gearboxes, pumps, fans, conveyors and general industrial machinery, with fast shipping to Iraq, Saudi Arabia, UAE, Egypt, Yemen, Libya and across the Middle East and Africa.
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