Every week someone walks into the shop with a dead bearing in a plastic bag and asks "do you have one like this?" Nine times out of ten we can match it immediately — the part number is stamped on the inner ring. The other 10% of the time it's been run so hard the markings are gone, and that's when it becomes a measuring job.
Here's the order I measure bearings in, the mistakes to avoid, and how to decode the part number when the markings are readable.
The three numbers you need — in order
- Bore (d) — the inner ring's internal diameter. This is the shaft size the bearing fits on. Measure with a caliper or bore gauge across the inner ring.
- OD (D) — outer ring external diameter. This is the housing bore the bearing fits into. Caliper across the outer ring's outside.
- Width (B) — the bearing's thickness along the shaft axis. Parallel to the shaft.
All three in millimetres. Standard bearing catalogues are organised by bore first, then OD, then width — that's the order to remember.
Decoding the part number — 6205-2RS as an example
Let's break down "6205-2RS C3":
- 6 — type code. 6 = deep-groove ball. 7 = angular-contact. 3 = double-row. N = cylindrical roller.
- 2 — dimension series. Tells you the OD and width ratios relative to the bore.
- 05 — bore code. For codes 04 and above, multiply by 5 to get bore in mm. So 05 = 25mm bore.
- -2RS — suffix. Two rubber seals (one per side). Other common suffixes: -Z (metal shield one side), -2Z (shields both sides), open (no seal).
- C3 — radial internal clearance. C0 = normal (usually omitted), C3 = looser, C2 = tighter.
Suffixes — what -2RS, -C3, -P5 actually mean
| Suffix | Meaning | When you'd use it |
|---|---|---|
| -RS / -2RS | Rubber contact seal (one / both sides) | General industrial — dirt and moisture protection |
| -Z / -2Z | Metal shield (one / both sides) | Higher speeds, lower friction than RS |
| -C2 | Tighter-than-normal radial clearance | Very precise spindle applications |
| -C3 | Looser-than-normal radial clearance | High temperature, interference fit on shaft |
| -P5 / -P4 | Precision grade (higher than standard P6) | Machine-tool spindles, high-precision work |
| -E | Reinforced design — higher load rating | High-duty cylindrical roller applications |
When the markings are gone
If the bearing's been running contaminated and the part number has worn off:
- Measure bore with a caliper or bore gauge.
- Measure OD with a caliper.
- Measure width with a caliper.
- Count the rolling elements if possible — deep-groove balls have 7-10 balls typically; cylindrical rollers have 8-12 rollers.
- Note the seals/shields — rubber (RS), metal (Z), or open.
Write down all three dimensions and WhatsApp me. A deep-groove ball bearing's dimensions uniquely identify the part number — I can match it from bore/OD/width in under 30 seconds.
Common traps to avoid
- UC series (insert bearings). These have a wide inner ring with set screws. The part number (UC205, UC206) uses the same bore code as 6-series, but the outer ring is spherical. You cannot swap a UC205 with a 6205.
- Inch bearings. Older machinery and some imports use inch-sized bearings (R-series, RLS, Timken/SKF inch tapered-rollers). Measure in both mm and inches to be sure — a "25mm" bore might actually be 1" (25.4mm).
- Thrust vs radial. If the bearing has flat washers instead of a curved groove, it's a thrust bearing — don't swap with a radial ball bearing.
- Sealed vs shielded. Not always interchangeable. Rubber seals run slightly hotter and slower; metal shields run faster and cooler. Match the original on high-speed or high-duty applications.
When in doubt, bring the bearing to Shri Narayan Machinery LLP at Sector 9, Noida or send a clear photo with the markings visible to +91-9811104037. 90% of the time I can identify the part number and quote in one reply.