How do I read the bore from a bearing number?

For codes 04 and above, multiply the last two digits by 5 to get the bore in millimetres — 6204 has a bore of 4 times 5, which is 20 mm. The codes 00, 01, 02, 03 are special and mean 10, 12, 15, and 17 mm respectively.

What does the first digit mean?

It identifies the bearing type. 6 is a single-row deep-groove ball bearing, 1 is self-aligning, 2 is spherical roller, 3 is angular-contact or tapered, 7 is angular-contact ball, and N is cylindrical roller. The 6-series is by far the most common.

What is the difference between 6204 and 6304?

Both have a 20 mm bore but belong to different dimension series. The second digit (2 versus 3) sets how large and heavy the bearing is: a 6304 has a bigger outside diameter and width than a 6204, so it carries more load at the same bore.

Why does 6200 mean a 10 mm bore?

The two-digit bore code is only a direct times-5 multiplier from 04 upward. The four low codes were assigned fixed bores historically: 00 = 10, 01 = 12, 02 = 15, 03 = 17 mm. This is a quirk worth memorising.

Are these dimensions standard across brands?

Yes. ISO 15 fixes the boundary dimensions — bore, outside diameter, and width — so a 6204 from any reputable manufacturer interchanges dimensionally. Internal clearance, seals, and precision class are coded by suffixes not covered here.

Bearing Number Reference

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A metric bearing number is a compact code for its type and size. This tool reads the ISO 15 designation, decodes the type and dimension series, expands the bore code into millimetres, and matches the boundary dimensions from a table of common bearings.

How it works

The number is read digit by digit. The first digit (or letter) is the bearing type. The second is the dimension series — larger series numbers mean a heavier bearing for the same bore. The final two digits are the bore code:

if code >= 04:  bore = code * 5  (mm)
00 -> 10 mm   01 -> 12 mm   02 -> 15 mm   03 -> 17 mm

So 6204 decodes as: type 6 (deep-groove ball), series 2 (light), bore code 04 → 20 mm bore. The outside diameter and width come from the standard boundary table because they depend on both the bore and the series.

Tips and notes

The four low bore codes (00–03) break the times-5 rule — memorise 10, 12, 15, 17 mm.
Same last two digits, different series digit, means same bore but different OD and load rating (6204 vs 6304).
Boundary dimensions are standardised, so any-brand replacements of the same number fit; suffixes like 2RS or C3 describe seals and clearance, not size.
This tool covers the common 6000/6200/6300 deep-groove families; other types share the same numbering logic.