MPNbase

20×52×21 mm bearings

9 models from 2 brands across 3 types share this ISO 15 envelope: 20 mm bore, 52 mm outside diameter, 21 mm width (0.787×2.047×0.827 in), 16 mm radial section.

9 models fit this space 2 brands 9 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)
2304 Self-Aligning Ball NTN open — 18.5 4.7 207
2304-E-2RS1TN9 Self-Aligning Ball SKF 2RS CN 14.3 4 210
2304-TN9 Self-Aligning Ball SKF open CN 18.2 4.75 220
2304K Self-Aligning Ball NTN open — 18.5 4.7 207
4304-ATN9 Deep Groove Ball SKF open CN 23.4 16 210
62304-2RS Deep Groove Ball SKF 2RS CN 15.9 7.8 210
NJ2304-ECP Cylindrical Roller SKF open CN 47.5 38 220
NU2304-ECP Cylindrical Roller SKF open CN 47.5 38 210
NUP2304-ECP Cylindrical Roller SKF open CN 47.5 38 220

Note: catalogue dynamic load ratings for this envelope span 14.3– 47.5 kN — a 232% spread between designs in the very same 20×52×21 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 20 mm bore bearings for wider or narrower sections, or open a model page for naming-rule decode, applications and graded cross references: 2304, 2304-E-2RS1TN9, 2304-TN9, 2304K, 4304-ATN9, 62304-2RS, NJ2304-ECP, NU2304-ECP, NUP2304-ECP.

Frequently asked questions

Are all 20×52×21 mm bearings interchangeable?

They share the same ISO 15 boundary dimensions — 20 mm bore, 52 mm OD, 21 mm width (0.787×2.047×0.827 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 20×52×21?

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 20×52×21 mm in inches?

20×52×21 mm converts to 0.787×2.047×0.827 in, with a 16 mm (0.630 in) radial section height. These are the ISO 15 general-plan envelope dimensions shared across manufacturers, which is why models such as 2304, 2304-E-2RS1TN9, 2304-TN9 mount in the same space despite different internal designs.