Comparison
62 vs 63 series bearings: light vs medium explained
Why a 6205 and a 6305 share a 25 mm bore but not a housing: how the 62 (light) and 63 (medium) series differ, with dimension tables and selection guidance.
A 6205 and a 6305 both fit a 25 mm shaft, and both are deep groove ball bearings. They are often listed next to each other, and buyers regularly ask whether one can replace the other. The short answer is no — not without changing the housing. This comparison explains why.
What the second digit means
In a deep groove ball bearing number, the first digit is the bearing type (6), the second digit is the diameter series, and the last two digits are the bore code. The diameter series sets how big the bearing’s cross-section is for a given bore:
| Series | Diameter series | Section | Example (25 mm bore) |
|---|---|---|---|
| 60 | 0 | Extra light | 6005 — 25 × 47 × 12 mm |
| 62 | 2 | Light | 6205 — 25 × 52 × 15 mm |
| 63 | 3 | Medium | 6305 — 25 × 62 × 17 mm |
| 64 | 4 | Heavy | 6405 — 25 × 80 × 21 mm |
Moving from 62 to 63 keeps the bore and increases both the outside diameter and the width. The rings get thicker and the balls get larger.
Side by side
| Bore | 62 series (light) | 63 series (medium) | OD difference | Width difference |
|---|---|---|---|---|
| 17 mm | 6203 — 17 × 40 × 12 | 6303 — 17 × 47 × 14 | +7 mm | +2 mm |
| 20 mm | 6204 — 20 × 47 × 14 | 6304 — 20 × 52 × 15 | +5 mm | +1 mm |
| 25 mm | 6205 — 25 × 52 × 15 | 6305 — 25 × 62 × 17 | +10 mm | +2 mm |
| 30 mm | 6206 — 30 × 62 × 16 | 6306 — 30 × 72 × 19 | +10 mm | +3 mm |
| 40 mm | 6208 — 40 × 80 × 18 | 6308 — 40 × 90 × 23 | +10 mm | +5 mm |
| 50 mm | 6210 — 50 × 90 × 20 | 6310 — 50 × 110 × 27 | +20 mm | +7 mm |
A neat side effect of the standard dimension plan is that some sizes line up across series: the outside diameter of a 6305 (62 mm) equals the outside diameter of a 6206, and a 6304 has the same 52 mm OD as a 6205. They still have different bores and widths, so they are not substitutes either.
What changes with the heavier section
Because the medium series uses larger balls and thicker rings, it generally offers:
- higher load capacity for the same shaft size;
- more tolerance of shock loads and heavier-duty service;
- a larger, heavier bearing that needs more housing space.
The light series is lighter and more compact, and it is the most widely stocked deep groove ball bearing series. For many general applications — fans, small motors, pumps, household machinery — it is the default.
We deliberately do not quote load ratings here: they depend on the manufacturer and the internal design of the exact bearing, so compare the datasheets of the specific products you are considering.
Can you replace a 6205 with a 6305?
Not directly. The 6305 is 10 mm larger in outside diameter and 2 mm wider, so it will not fit a housing machined for a 6205. Going the other way, a 6205 would be loose in a 6305 housing. Changing series is a design change: it means a different housing bore, possibly a different shoulder height on the shaft, and a fresh look at the load and life calculation.
The same logic applies across bearing types. A 1205, 7205 or NU205 has exactly the same 25 × 52 × 15 mm envelope as a 6205, but carries loads differently. Same dimensions are not the same function — our comparison of exact match, variant and candidate substitute explains how to keep those relationships separate in data.
The same pattern in other bearing types
The 2/3 split repeats throughout the standard dimension plan:
| Type | Light (diameter series 2) | Medium (diameter series 3) |
|---|---|---|
| Deep groove ball | 62xx | 63xx |
| Self-aligning ball | 12xx | 13xx |
| Angular contact ball | 72xx | 73xx |
| Cylindrical roller | NU2xx | NU3xx |
| Spherical roller | 222xx | 223xx |
Within each type, the light and medium series for the same bore code have different outside diameters and widths — exactly as with 62 and 63.
Apply it
Compare sizes on the bearing size chart, or open any size page — each one lists every other standard bearing with the same bore. If your catalog mixes 62 and 63 bearings under loose descriptions such as “25 mm bearing”, matching and deduplication shows how to separate them reliably. Questions about your data? Contact us.
Methodology article using synthetic examples only; it states no manufacturer specifications. Independent technical review: not yet assigned. Found an error? Tell us.
