7321B bearing: complete specifications & equivalents
The 7321B 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 | 224 kN |
| Basic static load rating C0 | 194 kN |
| Fatigue load limit Pu | 11.8 kN |
| Limiting speed (mechanical) | 2900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 8360 g |
| Manufacturer designation | NTN 7321B |
| 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 | — |
| 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 |
|---|---|---|---|
| 7321B | 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 7321B model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 7321B appears as a heavy-duty 7300 single-row family bearing of 105 mm bore, 225 mm outside diameter and 49 mm width. NTN builds the number from 73 is the single-row dimension series (heavy-duty 7300 single-row family), then 21 encodes the 105 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 mass is about 8360 g, which at this 60.0 mm radial section keeps the bearing comfortably inside high-speed spindle weight budgets. If the duty is mainly high speed with modest thrust, the 7900-series cross-section is the lighter alternative; if thrust dominates, the 7300-series section carries more. 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
- 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
- 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
- loss of preload after housing-fret or shaft creep, leaving the pair loose — ball skidding, cage rattle and a falling natural frequency follow
- resin-cage cracking on the 7900-series sizes after hot, dry running or solvent attack on the polymer
- current-erosion pitting on VFD-driven motor shafts, first visible as a grey frosted band across both raceways
- 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
- 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 40 deg B-execution raises axial capacity but lowers the speed ceiling — do not copy the standard-bearing speed and preload settings onto it.
- Grease rated for deep-groove motor duty is not automatically right at 2,900 r/min with preload; check the grease speed factor against the catalogue figure.
- Catalogue mass and ratings belong to the open execution; shields, seals and resin cages change both the speed ceiling and the thermal behaviour of the same basic size.
- If the application vibrates at standstill (transport, idle machine next to a running line), specify protection: the contact ellipse of a preloaded bearing false-brinells faster than a loose one.
- The 224/194 kN ratings and 11.8 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7321B; 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 7321B?
7321B 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 224 kN, C0 194 kN and a 11.8 kN fatigue load limit Pu; the grease limiting speed is 2,900 r/min and the oil rating 3,800 r/min; mass about 8360 g.
How is the 7321B 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), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). The 225 mm OD and 49 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7321B support?
One 7321B 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 7321B?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 2,900 r/min and the oil rating 3,800 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 7321B?
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 224 kN / C0 194 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.