Cylindrical roller bearing · NU3 series
NU321 bearing
105 × 225 × 49 mm
The NU321 is a cylindrical roller bearing with a 105 mm bore, 225 mm outside diameter and 49 mm width. NJ321, NUP321, N321 share these boundary dimensions with a different flange arrangement. Medium series; NJ3, NUP3 and N3 share these dimensions.
- Bore d
- 105 mm 4.1339 in
- Outside diameter D
- 225 mm 8.8583 in
- Width B
- 49 mm 1.9291 in
- Dimension series
- 03
- Load directions
- High radial; NJ/NUP limited axial
Designation explained
What NU321 means
Standard bearing numbers encode the type, the dimension series and the bore. Anything after the base number — seals, clearance, cage — is a suffix.
| Part | Meaning |
|---|---|
NU | Cylindrical roller bearing, two flanges on the outer ring, none on the inner ring (NJ, NUP and N are other flange arrangements) |
3 | Dimension series 03 |
21 | 21 → 105 mm bore (21 × 5) |
Variants
Common NU321 variants
Suffixes change the bearing without changing its boundary dimensions. The exact letters differ between manufacturers — always order by the full designation from the maker you choose.
| Suffix | Example | Meaning |
|---|---|---|
NJ / NUP / N | NJ321 | Other flange arrangements with the same d × D × B — they locate the shaft differently and are not interchangeable without checking |
E / EC | NU321E | Reinforced internal design with more or larger rollers (higher load rating) |
M / P / J | NU321-E-M1 | Cage: brass (M), polyamide (P / TVP) or pressed steel (J) |
CN (no suffix) | NU321 | Normal internal clearance |
C3 | NU321-C3 | Internal clearance greater than normal — common for electric motors and heated shafts |
C4 | NU321-C4 | Internal clearance greater than C3 |
Same envelope
Same 105 × 225 × 49 mm, different type
These bearings have exactly the same bore, outside diameter and width but are a different type. They fit the same housing and shaft, but carry loads differently — same size is not the same function.
Same bore
Other 105 mm bore bearings
Every standard bearing in this reference with a 105 mm bore, from light to heavy sections.
Where to buy
Find NU321 at sellers
Search results on independent sellers. We are not affiliated with them, do not earn from these links and do not see their prices or stock. Results mix brands and variants — check the full designation before you order.
About these dimensions. Boundary dimensions follow ISO 15 (radial bearings — boundary dimensions, general plan), dimension series 03, and are the same for every manufacturer of a standard NU321. Chamfers, load ratings, speed limits and weight depend on the manufacturer and design and are not shown — use the maker's datasheet for engineering decisions. Last checked 9 October 2026. Spotted an error? Tell us.
Learn more
What size is a NU321 bearing?
A NU321 is a cylindrical roller bearing with a 105 mm bore, 225 mm outside diameter and 49 mm width (105 × 225 × 49 mm). These boundary dimensions follow the ISO dimension plan, so they are the same across manufacturers.
Is NJ321 the same as NU321?
NJ321, NUP321, N321 have the same bore, outside diameter and width as NU321, but different ring flanges. They guide the shaft axially in different ways, so swapping them changes how the arrangement works.
Can I replace NU321 with another bearing of the same size?
Other bearing types can share the same 105 × 225 × 49 mm envelope, but a different type has different load directions, speed limits and mounting needs. Same dimensions alone do not make two bearings interchangeable.
Where are the load ratings and speed limits?
They depend on the manufacturer and internal design, so we do not list a single value. Check the datasheet for the exact full designation you intend to use.
Need NU321 data for a whole catalog?
We can help with that.
Normalized specifications, variants and supplier listings for every bearing you sell, with the source behind each value.