7921 bearing: complete specifications & equivalents
The 7921 is a ISO 15 radial bearing sized 105 x 145 x 20 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 | 145 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 54 kN |
| Basic static load rating C0 | 54.5 kN |
| Fatigue load limit Pu | 3.25 kN |
| Limiting speed (mechanical) | 4400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 972 g |
| Manufacturer designation | NTN 7921 |
| 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 & 7900-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 5.709 in |
| Width B | 0.787 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 20 mm |
| Smallest bore in 7900-series | 25 mm |
| Largest outer diameter in 7900-series | 420 mm |
| Width range across 7900-series | 9–56 mm |
| Bore position in 7900-series (smallest first) | 17 of 32 |
| Bore above smallest 7900-series size | 80 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7921 | 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 7921 model number is decoded
From the extra-light, high-speed 7900 single-row family, 7921 measures 105 mm across the bore, 145 mm over the outer ring and 20 mm across the faces. Reading the code: 79 is the single-row dimension series (extra-light, high-speed 7900 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 30 deg contact angle is the lever that turns the 54.5 kN static rating into useful one-direction thrust capacity. The 105/145/20 envelope is an ISO 15 boundary plan, so dimensional interchange with other makers holds — ratings and internal geometry do not automatically follow. 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
- paper-machine roll and calendar drives
- extruder and mixer gearbox output shafts
- mining conveyor head-shaft positions
- marine auxiliary and winch gearbox shafts
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
- 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
- edge loading and early spalling from housing bores that are out of round or shoulders that are too small for the ring face
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 7900 extra-light section is chosen for speed and stiffness, not for load margin — check that C0 54.5 kN really covers the worst static case before substituting it for a 7000.
- A 7921 mounted the wrong way round still turns smoothly by hand; the failure shows up weeks later as raceway flaking on the unloaded-looking side.
- The C0 of 54.5 kN is a static rating, not a permissible running thrust — sizing continuous axial load from C0 alone is a recurring drawing-office error.
- A 7921 mounted the wrong way round still turns smoothly by hand; the failure shows up weeks later as raceway flaking on the unloaded-looking side.
- The 54/54.5 kN ratings and 3.25 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7921; 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 7921?
7921 is a single-row angular contact ball bearing to ISO 15: 105 mm bore, 145 mm outside diameter, 20 mm width (4.134 x 5.709 x 0.787 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 54 kN, C0 54.5 kN and a 3.25 kN fatigue load limit Pu; the grease limiting speed is 4,400 r/min and the oil rating 5,900 r/min; mass about 972 g.
How is the 7921 designation structured?
79 is the single-row dimension series (extra-light, high-speed 7900 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 145 mm OD and 20 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7921 support?
One 7921 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 7921?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 4,400 r/min and the oil rating 5,900 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 7921?
The 105/145/20 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 54 kN / C0 54.5 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.