NU320 bearing: complete specifications & equivalents
The NU320 is a ISO 15 radial bearing sized 100 x 215 x 47 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | Generic ISO interchange (unbranded) |
| Bore diameter d | 100 mm |
| Outer diameter D | 215 mm |
| Width B | 47 mm |
| Seal / shield | open |
| Internal clearance | CN / C3 / C4 available |
| Tolerance class | P0 |
| Cage | steel |
| Operating temperature | -30 to +120 °C |
| Mass (geometry estimate) | 6823 g |
| Standard | ISO 15 |
| Catalog version | iso15-crb-geometry |
| Last verified | 2026-09-24 |
Source: ISO 15 boundary-dimensions standard · extracted 2026-09-24
Standard-interchange bearing: dimensions per ISO 15; CN clearance, P0 tolerance and a stamped-steel cage are catalogue defaults unless the supplier states otherwise, and mass is a geometry-derived estimate. Brand catalogue load ratings and limiting speeds for NU320 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & NU300-series range
| Bore d | 3.937 in |
|---|---|
| Outer diameter D | 8.465 in |
| Width B | 1.85 in |
| ISO bore code | 20 |
| Radial section height (D−d)/2 | 57.5 mm |
| Smallest bore in NU300-series | 20 mm |
| Largest outer diameter in NU300-series | 215 mm |
| Width range across NU300-series | 15–47 mm |
| Bore position in NU300-series (smallest first) | 17 of 17 |
| Bore above smallest NU300-series size | 80 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NU320 model number is decoded
In the NU300-series (ISO 15 dimension series) the leading NU marks a single-row cylindrical roller: the outer ring has two integral shoulders and the inner ring none, so the inner-ring/roller assembly floats axially both ways and the bearing locates radially only; the last two digits of NU320 are bore code 20 = 100 mm (code × 5 from 04 upward). The ISO 15 envelope is 215 mm outside diameter and 47 mm width — 3.937 × 8.465 × 1.85 in, with a 57.5 mm radial section height. Straight cylindrical rollers give line contact for high radial capacity at low friction, with no self-alignment; catalogue practice for a rotating inner ring is a k5 shaft seat, H7 housing and C3 clearance. NJ adds one inner shoulder (one-direction location), NUP two shoulders (full location); E denotes a reinforced roller complement — verify against the actual load direction.
Typical equipment & failure modes
Common applications
- heavy crane and winch drums
- large fan and paper machine rolls
- rolling mill roll necks and chocks
- large gear drives and reducer shafts
- cement and mining machinery drives
Known failure patterns
- thermal seizure when an interference fit plus hot running removes all residual C3 clearance
- roller and raceway smearing when a lightly loaded NU row skids at start-up or below the minimum load
- edge loading and rib spalling from shaft-to-housing misalignment — cylindrical rollers run on line contact and cannot self-align
- roller-end and flange scoring when an NU bearing is forced to locate axially; only NJ/NUP designs carry thrust at the shoulders
- cage fatigue and fracture after sustained over-speed with marginal lubrication
Selection pitfalls — read before you substitute
- The large 100 mm-bore NU320 mounts with substantial force: heat the inner ring or use hydraulic equipment, support the 215 mm outer ring squarely, and plan lifting fixtures for the 47 mm-wide roller assembly — drifting it in cold brinells the line-contact raceways.
- The NU3 medium series at 100 mm bore uses the 215 mm OD and 47 mm width for heavy radial load; it needs stiffer shaft and housing shoulders and runs lower limiting speed than an NU220, so it is a poor choice in a high-rpm gearbox stage sized for the light row.
- Check the shoulder geometry for NU320: a generous fillet on the 100 mm shaft looks strong but stops the inner ring seating home; use the catalogue corner-relief radius and a withdrawal groove so the outer ring presses flush in the 215 mm, 47 mm-wide housing bore.
- Large NU320 rings need real draw-up force: use a sleeve or hydraulic press against the inner ring face only, verify the 100 mm seat temperature before assembly, and never strike the roller cage — a dented cage window on the 47 mm-wide set locks the rollers at the first hot run.
- Read the damage on a removed NU320: uniform roller smearing points to minimum-load skidding, while spalling on one edge of the 215 mm raceway means misalignment or a tilted housing face — the two failures need opposite corrections, so inspect before ordering the replacement fit.
- Order clearance for the fit: a rotating interference inner ring on a 100 mm shaft plus thermal growth consumes CN play, so C3 is the normal industrial default and C4 serves hot or vibratory mounts; CN suits loose outer-ring floating arrangements in bored housings.
- The E suffix denotes a reinforced design with larger rollers and higher rating than the basic NU320; never pair a standard and an E row on the same shaft — unequal stiffness splits the load unevenly, and the two are not life-equivalent despite the same envelope.
Frequently asked questions
What are the dimensions of an NU320 cylindrical roller bearing?
An NU320 single-row cylindrical roller bearing per ISO 15 has a 100 mm bore, 215 mm outer diameter and 47 mm width (3.937 × 8.465 × 1.85 in), a 57.5 mm radial section and roughly 6823 g geometry-based estimated mass; catalogue masses vary with cage and E design.
How does the NU320 bore code work?
The letters give the ring/shoulder design (NU = axially free, NJ = one inner shoulder, NUP = two shoulders) and the last two digits are bore code 20: 20 × 5 = 100 mm. The 215 mm OD and 47 mm width come from the ISO 15 dimension series (NU300), which shares its boundary plan with the 6-series deep-groove envelopes.
What is the difference between NU, NJ, N and NUP designs?
NU (like the NU320) has a shoulderless inner ring and floats axially in both directions; NJ has one integral inner-ring shoulder and locates the shaft in one direction; N has two inner shoulders and a shoulderless outer ring (mirror of NU); NUP adds a second, loose shoulder so the inner ring locates in both directions. Select by the shaft locating scheme, not by load rating — the envelopes are identical.
Can an NU320 take axial load or misalignment?
No thrust in the NU design: any sustained axial force scores the roller ends and ring flanges, so locate the shaft with an NJ/NUP row, a paired angular-contact bearing or a deep-groove row elsewhere. Misalignment is likewise not tolerated — line contact between cylindrical rollers and raceways edges under even small angular errors; use a spherical roller bearing where shaft deflection or housing misalignment is expected.
What does the E suffix mean and which clearance should be ordered?
E (as in NU320E) is the reinforced design: larger/optimised rollers raise the basic load rating over the basic designation in the same 100×215×47 mm envelope. For clearance, C3 is the usual default with an interference fit on a rotating inner ring because fit and thermal growth reduce residual play; use CN mainly for loose floating outer-ring mounts and C4 for hot or vibratory duty.
Reviewed & verified by the MPN Base engineering desk against source catalog iso15-crb-geometry on 2026-09-24. Read our editorial & correction policy.