Industrial bearings follow standardised numbering systems so that bore, type, and options can be identified from the marking on the ring or packaging. For procurement teams in the UAE, reading the designation correctly is the fastest path to an exact replacement — especially when equipment is imported from Europe, Asia, or the Americas and multiple brand equivalents exist. This guide covers deep groove ball bearings, roller types, and housed units most commonly requested for MRO and project supply.
Deep groove ball bearing format (ISO 15 / SKF)
The most common industrial bearing is the single-row deep groove ball bearing. The designation follows a pattern where the first digit identifies bearing type, the second digit identifies diameter series, and the last two digits encode bore size.
For bore codes 04 and above, multiply the last two digits by 5 to get bore diameter in millimetres. Example: 6205 → type 6 (deep groove ball), series 2 (light), bore code 05 → 5 × 5 = 25 mm bore.
| Designation | Bore (mm) | Typical use |
|---|---|---|
| 6204 | 20 | Small motors, fans |
| 6205 | 25 | Electric motors, pumps |
| 6208 | 40 | Conveyor drives, gearboxes |
| 6308 | 40 | Heavier radial load, medium series |
| 6310 | 50 | Pumps, compressors, larger motors |
| 6312 | 60 | Material handling, process equipment |
Bore codes below 04 (non-standard bore table)
Small bore bearings use direct codes rather than the ×5 rule. This catches many buyers off guard when replacing compact equipment bearings.
| Last two digits | Bore (mm) |
|---|---|
| 00 | 10 |
| 01 | 12 |
| 02 | 15 |
| 03 | 17 |
| 04 | 20 |
Sealing and shield suffixes
Letters after the base number describe sealing, lubrication, and special features. The same base number can exist in open, shielded, and sealed versions — they are not interchangeable in contaminated environments.
When requesting quotes, always include the suffix. A 6205-2RS (sealed) is a different stock item from 6205-2Z (shielded) or 6205 (open).
| Suffix | Meaning | Typical environment |
|---|---|---|
| (none) | Open bearing | Clean, re-lubricated regularly |
| -Z / -2Z | Shield one / both sides | Semi-clean indoor |
| -RS / -2RS | Contact seal one / both sides | Dusty, humid, outdoor |
| -RSH | SKF seal variant | Same as RS — brand-specific |
| C3 | Increased internal clearance | Hot ambient, tight shaft fit |
| M / MA | Brass cage | Roller bearings, higher temp |
Angular contact and roller designations
Angular contact ball bearings start with 7 (e.g. 7205, 7308) and are used where combined radial and axial loads exist — machine tool spindles, precision gearboxes, and paired mounting arrangements.
Cylindrical roller bearings use alpha prefixes: NU (outer ring guided), NJ (inner ring guided), NUP (locating bearing). Tapered roller bearings use 302xx and 303xx series numbers where the last digits relate to bore sizing under ISO standards.
- NU 205 ECP — 25 mm bore cylindrical roller, polyamide cage
- 30208 — tapered roller, commonly used in wheel hubs and industrial gearboxes
- 22208 E — spherical roller, tolerates misalignment in heavy equipment
Housed unit naming (UCP, UCF, UCFL)
Pillow blocks and flange units combine a bearing insert (typically UC series) with a cast housing. The number after the prefix indicates bore size using the same bore code logic as ball bearings — UCP 205 = 25 mm bore, UCP 208 = 40 mm bore.
Confirm housing style: UCP (two-bolt pillow block), UCF (four-bolt square flange), UCFL (two-bolt oval flange), UCT (take-up unit). The insert and housing are often ordered together but can be replaced separately on maintenance.
When the marking is missing or unreadable
If the designation is worn off, measure bore (d), outside diameter (D), and width (B) in millimetres with calipers. Provide load direction (radial, axial, or combined), shaft speed, and application (motor, conveyor, pump, etc.).
Photos of the bearing, housing, and equipment nameplate significantly reduce back-and-forth during cross-reference — especially for mixed-brand plants across Dubai, Sharjah, and Abu Dhabi industrial zones.
Common mistakes to avoid
- Quoting 6205 when the existing bearing is 6205-2RS — sealing matters for life and contamination
- Assuming C3 clearance is always better — normal CN clearance is correct for most general drives
- Mixing inch and metric housed units without verifying bore
- Replacing roller bearings with ball bearings on heavy radial load applications
- Ignoring brand suffix differences when equipment manufacturer specifies exact designation
RFQ checklist
- Full designation including suffix (e.g. 6308-2RS C3)
- Brand on existing bearing if visible (SKF, FAG, NSK, etc.)
- Bore × OD × width (mm) if designation unknown
- Sealing requirement based on environment
- Load direction and approximate RPM
- Quantity and urgency (stock vs project lead time)