7321-NTN bearing: complete specifications & equivalents
The 7321-NTN is a ISO 15 radial bearing sized 105 x 225 x 49 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 49 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 244 kN |
| Basic static load rating C0 | 210 kN |
| Fatigue load limit Pu | 12.8 kN |
| Limiting speed (mechanical) | 3400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 8200 g |
| Manufacturer designation | NTN 7321 |
| 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 | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 1.929 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 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) | 22 of 32 |
| Bore above smallest 7300-series size | 95 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7321 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 7321-BECBP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 7321-BEP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 7321-DECBM | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
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 7321-NTN model number is decoded
The heavy-duty 7300 single-row family entry 7321 carries a 105 mm bore in a 225 mm outside diameter, 49 mm wide envelope. The designation breaks down as 73 is the single-row dimension series (heavy-duty 7300 single-row family); 21 encodes the 105 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. On speed, the grease limiting speed is 3,400 r/min and the oil rating 4,500 r/min. Selection starts from the thrust share: as axial load grows past roughly half the radial load, an angular-contact position of this section usually outlives a deep-groove one. Shaft and housing shoulders must clear the ring corners yet support enough face — the catalogue abutment diameters for the 105 mm bore give the working limits.
Typical equipment & failure modes
Common applications
- rolling-mill and metalworking drive shafts
- large pump, fan and compressor rotor shafts
- crane and hoist gearbox shafts
- paper-machine roll and calendar drives
Known failure patterns
- impact brinelling dents on the 30 deg contact path after a shaft-side hammer blow during mounting, because axial shock travels straight through the contact angle
- thermal runaway from excessive preload: the pair runs hot, grease darkens and the contact ellipse spreads until the raceways smear
- pressed-steel cage pocket wear and rivet loosening after repeated ball skid at light load and high speed
- flaking that starts at the raceway shoulder on the thrust-loaded side when axial load repeatedly exceeds the design share
- lubricant starvation scoring at the ball/raceway contact when grease volume or relubrication interval is guessed instead of calculated
Selection pitfalls — read before you substitute
- Bearings of 105 mm bore arrive heavy enough that handling damage (dents from slings, tilting on the shaft) is a real failure precursor — use proper lifting and heating kit.
- The standard 30 deg bearing and its B (40 deg) sibling share the envelope; picking between them is a load-direction decision, not a quality upgrade.
- The C0 of 210 kN is a static rating, not a permissible running thrust — sizing continuous axial load from C0 alone is a recurring drawing-office error.
- 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 C0 of 210 kN is a static rating, not a permissible running thrust — sizing continuous axial load from C0 alone is a recurring drawing-office error.
- The 244/210 kN ratings and 12.8 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7321; 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 7321?
7321 is a single-row angular contact ball bearing to ISO 15: 105 mm bore, 225 mm outside diameter, 49 mm width (4.134 x 8.858 x 1.929 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 244 kN, C0 210 kN and a 12.8 kN fatigue load limit Pu; the grease limiting speed is 3,400 r/min and the oil rating 4,500 r/min; mass about 8200 g.
How is the 7321 designation structured?
73 is the single-row dimension series (heavy-duty 7300 single-row family); 21 encodes the 105 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. The 225 mm OD and 49 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7321 support?
One 7321 alone takes thrust in one direction only, along its 30 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 7321?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 3,400 r/min and the oil rating 4,500 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 7321?
The 105/225/49 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 244 kN / C0 210 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.