Every bearing has a code stamped on it — something like SKF 6311-2RS1/C3 or Timken 25590. Learn to read bearing part numbers and you can identify any bearing's size, type, seals, and clearance without a catalog.
The core number: size and type
For metric ball and roller bearings, the last two digits of the core number give you the bore size: multiply by 5 to get millimeters. 6311 → 11 × 5 = 55 mm bore — that's our SKF 6311. (For bores under 20 mm the coding differs, but the ×5 rule covers the vast majority.)
The digits before that describe the series — width and diameter proportions:
- 62xx / 63xx: single-row deep groove ball bearings (63 = heavier series than 62) — e.g. SKF 6308, SKF 6305
- 60xx: extra-light deep groove ball bearings — e.g. SKF 6014
- 22xxx: spherical roller bearings — e.g. SKF 22210
- 32xxx / 33xxx: tapered roller bearings (metric series)
- 30xx: double-row angular contact ball bearings — e.g. SKF 3306
Prefixes: what comes before the number
Some brands add prefixes for design variants — SKF's E (e.g. 22210 E) means an optimized internal design with higher load capacity. Timken tapered bearings use a completely different 5-digit system (25590, 07100) where cone and cup are numbered separately.
Suffixes: seals, clearance, and more
This is where most confusion lives:
- Seals/shields: 2RS / 2RS1 / DDU / LLU = rubber seals both sides (see 6311-2RS1) · 2Z / ZZ = metal shields both sides (see 6308-2Z) · open (no suffix) = unsealed
- Clearance: C3 = greater than standard internal clearance, common in electric motors (see 6311/C3) · C4 = even greater · CN (often omitted) = standard
- Cage: JEM (SKF) = pressed steel cage · E = polyamide cage · M = brass cage
- Precision: P5, P6 = tighter tolerances than standard (P0)
Example: 6311-2RS1/C3 = 55 mm bore deep groove ball bearing, rubber sealed both sides, C3 clearance.
Why this matters when buying
Two bearings with the same core number can be very different parts. Ordering a "6311" when you need a "6311-2RS1/C3" gets you an open-clearance bearing that will fail early in a sealed, warm-running motor. Always match the full designation — or ask someone who knows the difference.
We speak bearing
Send RomTex Bearing & Supply any partial number, a photo of the markings, or just the dimensions — we'll identify it and match it to genuine NOS stock. Browse by part number or get in touch.