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. (If you'd rather not do it by hand, our free bearing number decoder and bearing finder by dimensions do both directions.)
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.