MPNbase

55×120×29 mm bearings

9 models from 4 brands across 5 types share this ISO 15 envelope: 55 mm bore, 120 mm outside diameter, 29 mm width (2.165×4.724×1.142 in), 32.5 mm radial section.

9 models fit this space 4 brands 6 with catalogue C rating

Dimensional interchange — verify before substituting

These bearings are interchangeable on boundary dimensions per ISO 15 — same bore, OD and width. They are not guaranteed drop-in equivalents: compare load ratings, seals, clearance, cage, precision and axial-locating design for the specific duty. Models without a catalogue C rating on this site carry ISO 15 geometry only; request the manufacturer table before a load-critical replacement.

Model Type Brand Seal Clearance C (kN) C0 (kN) Mass (g)
1311 Self-Aligning Ball NTN open — 51.5 17.9 1600
1311K Self-Aligning Ball NTN open — 51.5 17.9 1600
21311 Spherical Roller GENERIC-ISO open CN — — 1322
6311 Deep Groove Ball SKF open CN 74.1 45 1350
6311-2RS Deep Groove Ball SKF 2RS CN 74.1 45 1400
6311-RSR Deep Groove Ball NSK RSR CN 78.5 44.5 1370
6311-ZZ Deep Groove Ball SKF ZZ CN 74.1 45 1400
7311 Angular Contact Ball GENERIC-ISO open CN — — 1322
NU311 Cylindrical Roller GENERIC-ISO open CN — — 1322

Note: catalogue dynamic load ratings for this envelope span 51.5– 78.5 kN — a 52% spread between designs in the very same 55×120×29 mm space. The higher-rated unit is not an upgrade for every duty (it may run at lower limiting speed), but ignoring the gap will over- or under-life the replacement.

Substitution verification checklist

  1. Load rating. Check C (dynamic) and C0 (static) against the original life calculation — the table above shows which models carry verified catalogue values.
  2. Sealing. Open, -ZZ shields and -2RS contact seals are not equivalent in friction, speed or contamination protection; match the housing environment, not just the suffix on the old box.
  3. Internal clearance. CN/C3/C4 changes with fit and operating temperature; an interference inner-ring mount commonly needs C3 where the bench bearing ran CN.
  4. Cage and precision. Stamped steel, machined brass and polymer cages, and P0/P6/P5 tolerance classes, carry different speed and shock limits.
  5. Locating behaviour. Within one envelope an NU cylindrical roller floats axially while an NJ/NUP locates; ball designs take thrust that roller locating schemes do not. Preserve the shaft's locating arrangement.

Browse all 55 mm bore bearings for wider or narrower sections, or open a model page for naming-rule decode, applications and graded cross references: 1311, 1311K, 21311, 6311, 6311-2RS, 6311-RSR, 6311-ZZ, 7311, NU311.

Frequently asked questions

Are all 55×120×29 mm bearings interchangeable?

They share the same ISO 15 boundary dimensions — 55 mm bore, 120 mm OD, 29 mm width (2.165×4.724×1.142 in) — so they fit the same shaft, housing bore and axial space. Interchangeability ends at the envelope: dynamic load rating, seal arrangement, internal clearance, cage and precision class differ between the 9 models listed here and must be checked against the duty before substitution.

Is it a drop-in replacement if two bearings both measure 55×120×29?

Only after verification. Confirm five things in order: (1) the C/C0 load ratings meet the original life calculation, (2) the seal type is equivalent or acceptable for the contamination level (open vs -ZZ vs -2RS), (3) internal clearance matches (CN/C3/C4 — an interference fit changes residual play), (4) cage material and precision class suit the speed, and (5) the axial-locating behaviour is the same (for example an NU cylindrical roller floats while an NJ locates one way). Same dimensions alone never guarantee equal performance.

What is 55×120×29 mm in inches?

55×120×29 mm converts to 2.165×4.724×1.142 in, with a 32.5 mm (1.280 in) radial section height. These are the ISO 15 general-plan envelope dimensions shared across manufacturers, which is why models such as 1311, 1311K, 21311 mount in the same space despite different internal designs.