NU218 bearing: complete specifications & equivalents
The NU218 is a ISO 15 radial bearing sized 90 x 160 x 30 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 | 90 mm |
| Outer diameter D | 160 mm |
| Width B | 30 mm |
| Seal / shield | open |
| Internal clearance | CN / C3 / C4 available |
| Tolerance class | P0 |
| Cage | steel |
| Operating temperature | -30 to +120 °C |
| Mass (geometry estimate) | 2104 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 NU218 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & NU200-series range
| Bore d | 3.543 in |
|---|---|
| Outer diameter D | 6.299 in |
| Width B | 1.181 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 35 mm |
| Smallest bore in NU200-series | 20 mm |
| Largest outer diameter in NU200-series | 180 mm |
| Width range across NU200-series | 14–34 mm |
| Bore position in NU200-series (smallest first) | 15 of 17 |
| Bore above smallest NU200-series size | 70 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NU218 model number is decoded
In the NU200-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 NU218 are bore code 18 = 90 mm (code × 5 from 04 upward). The ISO 15 envelope is 160 mm outside diameter and 30 mm width — 3.543 × 6.299 × 1.181 in, with a 35.0 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
- rolling mill roll necks and chocks
- large gear drives and reducer shafts
- cement and mining machinery drives
- crusher eccentric and drum shafts
- heavy crane and winch drums
Known failure patterns
- 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
- fretting corrosion on an interference inner-ring seat that creeps under a loose fit
- false brinelling indentations at the roller pitch when an idle bearing sits in machine vibration
- inner-ring shoulder damage from cold mounting force transmitted through the roller set
Selection pitfalls — read before you substitute
- The large 90 mm-bore NU218 mounts with substantial force: heat the inner ring or use hydraulic equipment, support the 160 mm outer ring squarely, and plan lifting fixtures for the 30 mm-wide roller assembly — drifting it in cold brinells the line-contact raceways.
- The NU2 light series at 90 mm bore (160×30 mm) is the default gearbox cylindrical row; on the same bore an NU318 is larger with a much higher rating — do not replace a failed NU318 with an NU218 without re-rating L10 life.
- The 30 mm-wide NU218 seats against shaft and housing shoulders whose fillet must clear the ring chamfer: keep the corner radius inside the catalogue limit so the 90 mm bore and 160 mm OD faces abut square — an oversized radius lifts the ring and edge-loads the 35.0 mm section.
- For the interference inner ring of NU218, heat to 80–100 °C with an induction heater (never a flame) and slide it dry to the 90 mm shaft shoulder; the roller assembly is fitted separately, and hammering cold through the 160 mm ring dents the raceways.
- Read the damage on a removed NU218: uniform roller smearing points to minimum-load skidding, while spalling on one edge of the 160 mm raceway means misalignment or a tilted housing face — the two failures need opposite corrections, so inspect before ordering the replacement fit.
- Keep the minimum load above the skid threshold (catalogue rule of thumb roughly 1–2% of the dynamic rating); an unloaded NU218 on an idler or in a cold-start gearbox develops roller smearing, so add a spring preload or downsize the bearing if the duty is mostly empty.
- The rings of an NU218 are separable and supplied as a matched unit: never mix the outer ring of one bearing with the inner-ring/roller assembly of another — the raceway and roller complement are graded together, and cross-matching shortens life even at identical 90×160 dimensions.
Frequently asked questions
What are the dimensions of an NU218 cylindrical roller bearing?
An NU218 single-row cylindrical roller bearing per ISO 15 has a 90 mm bore, 160 mm outer diameter and 30 mm width (3.543 × 6.299 × 1.181 in), a 35.0 mm radial section and roughly 2104 g geometry-based estimated mass; catalogue masses vary with cage and E design.
How does the NU218 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 18: 18 × 5 = 90 mm. The 160 mm OD and 30 mm width come from the ISO 15 dimension series (NU200), 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 NU218) 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 NU218 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 NU218E) is the reinforced design: larger/optimised rollers raise the basic load rating over the basic designation in the same 90×160×30 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.