18685-18620 bearing: complete specifications & equivalents
The 18685-18620 is a ANSI ABMA 19.2 radial bearing sized 44.45 x 79.375 x 17.462 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 44.45 mm |
| Outer diameter D | 79.375 mm |
| Width B | 17.462 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 50.5 kN |
| Basic static load rating C0 | 56 kN |
| Limiting speed (mechanical) | 4600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 347 g |
| Manufacturer designation | NTN 4T-18685/18620 |
| Standard | ANSI ABMA 19.2 |
| Catalog version | NTN 2203E 2026-09-25 |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN 2203E 2026-09-25) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN 2203E 2026-09-25); 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 & 4t-inch-series range
| Bore d | 1.75 in |
|---|---|
| Outer diameter D | 3.125 in |
| Width B | 0.687 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 17.5 mm |
| Smallest bore in 4t-inch-series | 12.7 mm |
| Largest outer diameter in 4t-inch-series | 260 mm |
| Width range across 4t-inch-series | 10.998–77.788 mm |
| Bore position in 4t-inch-series (smallest first) | 51 of 148 |
| Bore above smallest 4t-inch-series size | 31.750000000000004 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 18685 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; brand-specific OEM equivalents (NSK/FAG/NTN) pending multi-source data. |
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 18685-18620 model number is decoded
4T-18685/18620 is an NTN inch-series single-row tapered roller bearing: a separable cone-and-cup pair on the ABMA inch boundary plan, 44.45×79.375×17.462 mm (assembled width T), for a shaft of about 44.45 mm (1.75 in). Reading the designation: 4T-18685/18620 follows the ABMA inch convention — the number before the slash is the cone (inner ring with roller set and cage), the number after the slash is the cup (outer ring), and the pure-numeric inch family lettering ties the pair to its boundary plan. Grease relubrication at the 4,600 r/min limiting speed targets the cone-rib contact; sustaining 6,200 r/min needs an oil supply directed at the large roller ends. Cup-side note for 18620: within the pure-numeric inch family tables the 18685 cone is listed against several cup options, and it is the cup that fixes the 79.375 mm OD and the 17.462 mm assembled width — quote the full 18685/18620 pair, never the cone alone. Running clearance of 4T-18685/18620 is set at mounting by axial displacement of cone or cup — the catalogue does not ship a preloaded set, so the drawing must state end play or preload.
Typical equipment & failure modes
Common applications
- agricultural tractor transmission and PTO shafts
- industrial gearboxes built to inch shafting
- construction-equipment pivot and wheel positions
- mining and quarry conveyor drive pulleys
Known failure patterns
- rib-face scoring when the thrust share of the combined load exceeds what the cone rib of this size carries
- false brinelling on a stationary pair exposed to vibration during transport or standby
- preload loss and noise after one bearing of the adjusted pair is replaced without resetting end play
- cage damage from a mounting blow transmitted through the roller complement
- rolling-contact fatigue spalling after the catalogue L10 life at the actual combined load
Selection pitfalls — read before you substitute
- Hub and pinion positions of this 44.45 mm class are adjusted in pairs; verify end play against the axle or gearbox drawing and re-torque after bedding-in instead of trusting the first setting on 4T-18685/18620.
- The pure-numeric inch family at 44.45 mm bore (79.375×17.462 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 18685/18620 reference at purchase.
- Do not confuse T (17.462 mm, the assembled cone-plus-cup width) with the cone width when drawing spacers; an abutment sized to T leaves the cup unseated.
- Quote the full 18685/18620 pair at ordering: the 18685 cone also ships against sibling cups, and a cup from another reference changes the 17.462 mm assembled width and the rating.
- An unloaded 4T-18685/18620 near 4,600 r/min lets rollers skid and smear the cone rib; spring-preload lightly loaded high-speed pairs.
- The 50.5/56 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-18685/18620; internal geometry legitimately differs between inch-series makers, so re-verify ratings, adjustment and the exact cone/cup references before substituting another brand on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 4T-18685/18620?
4T-18685/18620 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 44.45 mm bore (1.75 in), 79.375 mm outside diameter and 17.462 mm assembled width T (3.125 × 0.687 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 50.5 kN, C0 56 kN, grease limiting speed 4,600 r/min, oil speed 6,200 r/min, mass about 347 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-18685/18620 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 18685 cone or the 18620 cup can be replaced by an identical reference from NTN or another ABMA-dimensioned maker. Pairing the cone with a different cup reference is a different catalogue row: OD, assembled T and the 50.5/56 kN ratings change with the cup.
What is the difference between 4T-18685/18620 and a metric ISO 355 tapered bearing?
4T-18685/18620 follows the ABMA inch boundary plan with cone/cup references; ISO 355 bearings use metric dimension-series numbers (302, 322, …). Even where a metric size looks close to 44.45×79.375×17.462 mm, the envelopes and contact angles differ — the two systems are not drop-in interchangeable; check every boundary value before substituting.
What does the 4T prefix on 4T-18685/18620 mean?
4T is NTN's tapered roller bearing quality mark, stamped on cone and cup in the factory. It identifies NTN's 4T programme and is not a dimension or variant code, so interchange lists quote the bare 18685/18620 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-18685/18620 list two speeds, 4,600 and 6,200 r/min?
The lower figure, 4,600 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 4T-18685/18620 at 6,200 r/min because oil removes rib-contact heat better. Real limits still depend on pair adjustment, oil flow and cooling.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN 2203E 2026-09-25 on 2026-10-01. Read our editorial & correction policy.