NU321 bearing: complete specifications & equivalents

Specification table

Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01

Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.

Cross references & equivalents

Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.

How the NU321 model number is decoded

NU321 is the standard section of the NTN NU300 dimension series for a 105 mm shaft — 355 kN of basic dynamic capacity in a 8330 g, open bearing. Reading the code: NU for the non-locating separable-inner-ring type, then the ISO 15 diameter/width series and the bore code — ×5 = 105 mm (00–03 use the 10/12/15/17 exception table). Minimum radial load matters: an unloaded NU321 at high speed skids its rollers and smears the raceway; spring preload or the rotor weight typically covers the requirement in motors and pumps. Equivalent-load planning treats NU321 as a pure radial bearing: keep P below 355 kN at the required L10, and let a paired angular-contact or thrust part carry any sustained axial component. Heat the inner ring to max 120 °C for the 105 mm interference fit and support the ring face square during fitting; cocking over a keyway brinells the raceway before first rotation.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Induction-heat the 105 mm inner ring (max 120 °C) and mount it before fitting the outer ring; the ring mass makes square guidance essential — driving through the rollers brinells the 225 mm raceway.
• Wide (22/23) and light (10/49) executions at 105 mm bore share bore but not OD/width; check the full NU300 series code before substituting, because housing and shoulder geometry will not interchange.
• The NU rib arrangement is not interchangeable with another prefix on the same 105 mm seat: outer ring ribbed, inner ring ribless. Swapping NU for NJ changes axial location behaviour even though the 225×49 mm envelope matches.
• The 60.0 mm section at 105 mm bore leaves a narrow oil path; with the standard cage the relubrication groove and oil-level design must keep grease from churning in the 49 mm-wide cavity.
• Do not replace NU321 with a deep-groove ball bearing on rating alone: line contact gives 355 kN radial capacity but the bearing cannot carry the thrust duty a ball bearing can and misalignment tolerance is only 3–4 arc-minutes.
• The 355/360 kN ratings, 37.5 kN Pu and 8330 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NU321 (standard execution); other makes sharing the ISO 15 envelope revise internal geometry without changing the order number, so keep the 2203E reference with the specification for critical drives.