MPNbase

55×78×16 mm bearings

3 models from 2 brands across 2 types share this ISO 15 envelope: 55 mm bore, 78 mm outside diameter, 16 mm width (2.165×3.071×0.630 in), 11.5 mm radial section.

3 models fit this space 2 brands 3 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)
51111 Thrust Ball NTN open — 35.5 85 247
51111-SKF Thrust Ball SKF open CN 30.2 81.5 230
81111-TN Cylindrical Roller Thrust SKF open CN 69.5 285 230

Note: catalogue dynamic load ratings for this envelope span 30.2– 69.5 kN — a 130% spread between designs in the very same 55×78×16 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: 51111, 51111-SKF, 81111-TN.

Frequently asked questions

Are all 55×78×16 mm bearings interchangeable?

They share the same ISO 15 boundary dimensions — 55 mm bore, 78 mm OD, 16 mm width (2.165×3.071×0.630 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 3 models listed here and must be checked against the duty before substitution.

Is it a drop-in replacement if two bearings both measure 55×78×16?

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 55×78×16 mm in inches?

55×78×16 mm converts to 2.165×3.071×0.630 in, with a 11.5 mm (0.453 in) radial section height. These are the ISO 15 general-plan envelope dimensions shared across manufacturers, which is why models such as 51111, 51111-SKF, 81111-TN mount in the same space despite different internal designs.