NA6918 bearing: complete specifications & equivalents
The NA6918 is a ISO 1206 radial bearing sized 90 x 125 x 63 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 90 mm |
| Outer diameter D | 125 mm |
| Width B | 63 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 172 kN |
| Basic static load rating C0 | 450 kN |
| Fatigue load limit Pu | 55 kN |
| Reference speed (thermal) | 3800 rpm |
| Limiting speed (mechanical) | 4300 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2300 g |
| Manufacturer designation | NA 6918 |
| Standard | ISO 1206 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & NA-69-series range
| Bore d | 3.543 in |
|---|---|
| Outer diameter D | 4.921 in |
| Width B | 2.48 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 17.5 mm |
| Smallest bore in NA-69-series | 12 mm |
| Largest outer diameter in NA-69-series | 130 mm |
| Width range across NA-69-series | 22–63 mm |
| Bore position in NA-69-series (smallest first) | 21 of 22 |
| Bore above smallest NA-69-series size | 78 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NA6918 model number is decoded
NA 6918 provides the full machined-ring needle roller construction: ground inner ring on a 90 mm seat, flanged outer ring at 125 mm, caged needles between them — the standard choice when a replaceable inner raceway is required. In SKF nomenclature the leading letters mark a machined-ring needle bearing with inner ring: figures state 90 mm d and 63 mm B, the 125 mm outside diameter from the dimension series 69 needle roller bearings with inner ring, and the 2RS suffix would add contact seals. Inner rings are separable: order replacement inner rings separately by d×D×B, since the outer ring and roller assembly survive journals that ruin an inner raceway. Minimum load matters: below roughly 0.02·C the rollers skid and smear; preloading the pivot or specifying a heavier execution avoids the glazing that pure oscillation produces on these raceways. Mounting: heat or press the inner ring onto the 90 mm k5 seat (max 120 °C), fit the flanged outer ring into the H7 housing bore, and check the 63 mm assembly for free rotation before applying load.
Typical equipment & failure modes
Common applications
- electric motor armature shafts with ground seats
- printing and paper-handling rollers
- gearbox shafts where the journal cannot be hardened on site
- wheel and lever pivots needing a replaceable inner ring
Known failure patterns
- needle edge loading and raceway denting when the shaft deflects beyond the compensation range
- polymer cage deformation when the local temperature exceeds the 120 °C sustained limit
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- corrosion pitting from condensation in intermittently operated machinery
- inner-ring raceway spalling after the narrow ring section runs hot with excessive interference
Selection pitfalls — read before you substitute
- Above 50 mm bore, thermal growth matters: the 90 mm inner ring or journal grows with temperature faster than the housing, and the small clearance of a needle roller contact leaves little reserve — check running clearance hot, not just at assembly.
- Reference and limiting speeds are different limits: the 3,800 r/min reference is the thermal criterion under load, The limiting value is mechanical; the reference value is thermal under load, and grease choice moves it substantially.
- Hardness is load capacity: in families without an inner ring the 90 mm journal must hold 58–64 HRC with a ground finish; a surface that looks fine but sits at 45 HRC will rib the raceway within weeks.
- The 172/450 kN ratings and 2300 g mass are SKF catalogue values transcribed from ch. 7.4 of PUB BU/P1 17000 (PDF table page 644); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
Which dimensions does the NA 6918 have?
A NA 6918 measures 90 mm bore/Fw × 125 mm outside diameter × 63 mm width (3.543 × 4.921 × 2.48 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 172 kN, static C0 450 kN, fatigue limit Pu 55 kN, limiting speed 4,300 r/min, reference speed 3,800 r/min, mass about 2300 g.
What does NA 6918 mean in SKF part numbering?
The letters mark a machined-ring needle roller bearing with inner ring: 90 mm bore, 63 mm width, 125 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Does the NA 6918 need a hardened and ground shaft?
Yes — that is the point of this family. The NA 6918 carries its own hardened, ground inner ring on a 90 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
What mounting mistakes ruin a NA 6918?
Mount the inner ring on the 90 mm seat first (induction heat, max 120 °C, or press), then fit the flanged outer ring into the H7 housing bore. Verify free rotation and, for 2RS executions, check the wider outer ring against the housing depth.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring on 2026-09-26. Read our editorial & correction policy.