How to Read Bearing Numbers — Size Guide for 608, 6001, 6202, and More
21 Mar 2026
Every bearing has a number stamped on its side — like 608ZZ or 6203-2RS. These aren't model numbers. They encode the bearing's type, size, and seal configuration in a standardized system. Once you learn to read them, you can determine the exact bore, outer diameter, and width without measuring.
How the Numbering Works
A bearing designation like 6203-2RS breaks down into three parts:
- Series prefix (62) — tells you the bearing type and cross-section
- Bore code (03) — tells you the inner diameter
- Suffix (2RS) — tells you the seal type
Bearing Series (First Digits)
| Series | Type | Cross-Section |
|---|---|---|
| 6 | Single row deep groove ball bearing | Standard |
| 60 | Extra light (thin section) | Narrow width |
| 62 | Light series | Medium width |
| 63 | Medium series | Wider, higher load |
| 7 | Angular contact ball bearing | — |
| N / NU | Cylindrical roller bearing | — |
| 51 | Thrust ball bearing | — |
Bore Code — How to Find the Inner Diameter
For bore codes 04 and above, multiply by 5 to get the bore diameter in mm:
- 04 → 4 × 5 = 20mm bore
- 05 → 5 × 5 = 25mm bore
- 06 → 6 × 5 = 30mm bore
For bore codes 00 to 03, use this lookup table:
| Code | Bore (mm) |
|---|---|
| 00 | 10mm |
| 01 | 12mm |
| 02 | 15mm |
| 03 | 17mm |
For single-digit codes (like 608), the last digit IS the bore in mm: 608 = 8mm bore.
Common Bearing Size Chart
| Bearing | Bore (ID) | Outer (OD) | Width | Common Use |
|---|---|---|---|---|
| 608 | 8mm | 22mm | 7mm | Skateboards, 3D printers (NEMA17 idler) |
| 625 | 5mm | 16mm | 5mm | 3D printer idler pulleys |
| 626 | 6mm | 19mm | 6mm | Small motors, power tools |
| 6000 | 10mm | 26mm | 8mm | Electric motors, pumps |
| 6001 | 12mm | 28mm | 8mm | Motors, gearboxes |
| 6002 | 15mm | 32mm | 9mm | Power tools, conveyors |
| 6003 | 17mm | 35mm | 10mm | Automotive, machinery |
| 6200 | 10mm | 30mm | 9mm | General purpose |
| 6201 | 12mm | 32mm | 10mm | Electric motors |
| 6202 | 15mm | 35mm | 11mm | Pillow blocks, fans |
| 6203 | 17mm | 40mm | 12mm | Gearboxes, conveyors |
| 6204 | 20mm | 47mm | 14mm | Automotive wheel hubs |
| 6205 | 25mm | 52mm | 15mm | Heavy machinery |
Suffix Codes — Seals and Shields
| Suffix | Meaning | Best For |
|---|---|---|
| ZZ (or 2Z) | Metal shields on both sides | Dust protection, runs at higher speeds |
| 2RS (or 2RZ) | Rubber seals on both sides | Moisture/water protection, slower speeds |
| Open | No seals or shields | Custom lubrication, high-speed applications |
Rule of thumb: Use ZZ (shielded) for dry, dusty environments. Use 2RS (sealed) for wet environments. Use open bearings only when you're maintaining your own lubrication system.
How to Measure a Bearing You Already Have
- Inner diameter (bore): Measure the hole with a caliper
- Outer diameter: Measure the full outer ring
- Width: Measure the thickness of the bearing
- Cross-reference with the chart above to find the bearing number
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