7304B bearing: complete specifications & equivalents
The 7304B is a ISO 15 radial bearing sized 20 x 52 x 15 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 20 mm |
| Outer diameter D | 52 mm |
| Width B | 15 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 19.2 kN |
| Basic static load rating C0 | 9.65 kN |
| Fatigue load limit Pu | 0.76 kN |
| Limiting speed (mechanical) | 13000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 141 g |
| Manufacturer designation | NTN 7304B |
| Standard | ISO 15 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.
Dimensions in inches & 7300-series range
| Bore d | 0.787 in |
|---|---|
| Outer diameter D | 2.047 in |
| Width B | 0.591 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 16 mm |
| Smallest bore in 7300-series | 10 mm |
| Largest outer diameter in 7300-series | 420 mm |
| Width range across 7300-series | 11–80 mm |
| Bore position in 7300-series (smallest first) | 5 of 32 |
| Bore above smallest 7300-series size | 10 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7304B | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 7304B model number is decoded
From the heavy-duty 7300 single-row family, 7304B measures 20 mm across the bore, 52 mm over the outer ring and 15 mm across the faces. NTN builds the number from 73 is the single-row dimension series (heavy-duty 7300 single-row family), then 04 encodes the 20 mm bore (bore code x 5), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). Catalogue dynamic rating C is 19.2 kN against C0 9.65 kN — a C0/C ratio of 0.50 that is typical of an angular-contact contact ellipse. For a 20 mm shaft with combined load, the practical shortlist is this series, its 7200-series lighter section, and — where thrust reverses — a back-to-back pair rather than a single row. Set preload or end-play with the pair as a unit and lock the adjustment; a single angular-contact bearing cannot run free like a deep-groove one.
Typical equipment & failure modes
Common applications
- small machine-tool spindle and live-centre positions
- high-speed router, grinder and woodworking spindles
- small pump and compressor shafts with combined load
- servo and stepper motor shafts with axial preload
Known failure patterns
- false brinelling on the raceway contact ellipses when a preloaded spindle sits vibrating at standstill — visible as evenly spaced flute-like wear at ball pitch
- thermal runaway from excessive preload: the pair runs hot, grease darkens and the contact ellipse spreads until the raceways smear
- resin-cage cracking on the 7900-series sizes after hot, dry running or solvent attack on the polymer
- contamination-induced denting — hard particles rolled into the contact ellipse become the initiation points for surface fatigue
- flaking that starts at the raceway shoulder on the thrust-loaded side when axial load repeatedly exceeds the design share
Selection pitfalls — read before you substitute
- At 20 mm bore the rings are thin-sectioned: press force must go through the ring being fitted, never through the balls, or the first damage is already in the raceway before the machine runs.
- The 40 deg B-execution raises axial capacity but lowers the speed ceiling — do not copy the standard-bearing speed and preload settings onto it.
- A single-row angular contact left loose on the shaft to "help assembly" will fret the seat: the contact angle keeps driving the ring axially under load.
- On a 20 mm shaft, an interference fit eats internal clearance; skipping the clearance/preload recalculation is the classic cause of a new bearing running 20 deg C hotter than the drawing suggests.
- Substituting the B (40 deg) execution for the standard 30 deg bearing changes the axial/radial load split — the shaft position and the mating bearing see different forces even though the envelope is identical.
- The 19.2/9.65 kN ratings and 0.76 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7304B; internal geometry legitimately differs between manufacturers, so re-verify ratings, contact angle and suffix before substituting another make on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 7304B?
7304B is a single-row angular contact ball bearing to ISO 15: 20 mm bore, 52 mm outside diameter, 15 mm width (0.787 x 2.047 x 0.591 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 19.2 kN, C0 9.65 kN and a 0.76 kN fatigue load limit Pu; the grease limiting speed is 13,000 r/min and the oil rating 18,000 r/min; mass about 141 g.
How is the 7304B designation structured?
73 is the single-row dimension series (heavy-duty 7300 single-row family); 04 encodes the 20 mm bore (bore code x 5), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). The 52 mm OD and 15 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7304B support?
One 7304B alone takes thrust in one direction only, along its 40 deg contact angle; reversing thrust calls for a second bearing or a factory-matched DB/DF/DT pair (the catalogue right-hand columns list the paired ratings). Radial load is always carried as a combined load through the angled contact.
What lubrication speeds does NTN print for 7304B?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 13,000 r/min and the oil rating 18,000 r/min. These are catalogue ceilings for a correctly mounted bearing with the stated lubricant; preload, fill quantity, ambient heat and paired arrangements all move the real limit.
What should be checked before substituting another make for 7304B?
The 20/52/15 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 19.2 kN / C0 9.65 kN, the speed figures, contact angle and suffix meaning against the donor catalogue before swapping on a rated drive.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.