ISO dimension series 03 · deep groove ball bearing

6304

A 6304 bearing measures 20 mm bore × 52 mm outside diameter × 15 mm width.

The basic number fixes the nominal boundary dimensions. It does not specify the seals, shields, internal clearance, cage, lubricant or precision class.

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Bore d: 20mm
Outside D: 52mm
Width B: 15mm

What does 6304 mean?

Single row deep groove ball bearing.

Series digit used in the basic designation. The formal ISO classification is width series 0 plus diameter series 3: dimension series 03.

Bore reference 04, which corresponds to 20 mm.

For bore codes 04 and above, multiply the final two digits by five to get the bore in millimetres. The four exceptions are 00 = 10 mm, 01 = 12 mm, 02 = 15 mm and 03 = 17 mm.

How does 6304 compare with the same-bore series?

Every row below fits the same 20 mm shaft, but requires a different housing diameter and axial width. They are not drop-in alternatives unless all three dimensions match the assembly.

Designation	Bore	Outside	Width	Envelope difference
6004	20 mm	42 mm	12 mm	-10 mm OD, -3 mm width
6204	20 mm	47 mm	14 mm	-5 mm OD, -1 mm width
6304This page	20 mm	52 mm	15 mm	Reference

Can another maker's 6304 replace it?

The nominal mounting envelope is standardised, so another maker's basic 6304 has the same 20 × 52 × 15 mm boundary dimensions. That does not make every variant functionally interchangeable. Match the complete marking, especially its closure and clearance suffixes, and check the manufacturer's current datasheet for a critical application.

Read the complete marking

1. Basic designation: confirms the bearing type and boundary dimensions.
2. Closure suffix: identifies open, shielded or sealed construction; codes vary by manufacturer.
3. Clearance suffix: identifies radial internal clearance, such as C3 where specified.
4. Other suffixes: can identify cage, lubricant, tolerance, temperature or special construction.

6304-N and 6304-NR snap-ring variants

In NSK's system, N means an outer-ring locating snap-ring groove; NR means the groove with its locating ring. This is not a DIN 471 shaft groove or DIN 472 housing groove. NSK lists this row within its ISO 464 locating-ring table.

a max: 2.46 mm
b min: 1.35 mm
D1 max: 49.73 mm
r0 max: 0.40 mm
rN min: 0.50 mm
D2 max: 57.90 mm
f max: 1.12 mm

Read the N vs NR and ISO 464 guide →

Identify the complete 6304 specification

Seals and shields C2, CN, C3 and C4 How to measure

Where these dimensions come from

The 20 × 52 × 15 mm figures were checked against NSK's published bearing data on 20 August 2026. ISO 15 is listed as the standards context; Axial Supply has not reproduced the standard itself.

NSK Rolling Bearings for Industrial Machinery, Part C, section 1 — Deep Groove Ball BearingsBoundary-dimension tables beginning at page C 005; the published rows were checked against the applicable table spread.
ISO 15:2017 — Rolling bearings — Radial bearings — Boundary dimensions, general planThe standards-level context for nominal radial-bearing boundary dimensions; the numerical values here were read from NSK's published tables.