K15X21X21 bearing: complete specifications & equivalents
The K15X21X21 is a DIN 5402 radial bearing sized 15 x 21 x 21 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 15 mm |
| Outer diameter D | 21 mm |
| Width B | 21 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 18.7 kN |
| Basic static load rating C0 | 24.5 kN |
| Fatigue load limit Pu | 3 kN |
| Reference speed (thermal) | 24000 rpm |
| Limiting speed (mechanical) | 26000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 17 g |
| Manufacturer designation | K 15x21x21 |
| Standard | DIN 5402 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.1 needle roller and cage assemblies |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.1 needle roller and cage assemblies) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.1 needle roller and cage assemblies); 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 & K-series range
| Bore d | 0.591 in |
|---|---|
| Outer diameter D | 0.827 in |
| Width B | 0.827 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 3 mm |
| Smallest bore in K-series | 3 mm |
| Largest outer diameter in K-series | 63 mm |
| Width range across K-series | 7–32 mm |
| Bore position in K-series (smallest first) | 11 of 22 |
| Bore above smallest K-series size | 12 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the K15X21X21 model number is decoded
SKF lists K 15x21x21 in the K series of needle roller and cage assemblies: needle rollers caged at 15×21×21 mm, designed to run directly on a ground, hardened shaft and inside a machined housing bore. In the K code K 15x21x21, Fw×E×B reads directly as journal 15 mm, complement diameter 21 mm and cage width 21 mm; the housing bore is ground to E with H6/H7 tolerance to complete the outer raceway. SKF supplies these assemblies in single rows as tabulated; the cage quality determines the speed ceiling, and the catalogued 26,000 r/min limiting speed assumes a precision ground journal and bore. Speed planning separates the two ceilings: 24,000 r/min thermal reference and 26,000 r/min mechanical limiting — needle bearings tolerate high rpm only with adequate lubricant film at the 15 mm seat. Mounting: grind the 15 mm journal to the catalogue raceway tolerance after hardening to 58–64 HRC, bore the housing to E 21 mm H6, and slide the assembly in axially — pressing through the cage distorts it and locks the rollers.
Typical equipment & failure modes
Common applications
- rocker arm and rocker pin pivots on camshafts
- pump and gearbox idler gears running on hardened pins
- hinge and pivot joints in printing and textile machinery
- universal joint crosses on commercial vehicles
Known failure patterns
- raceway spalling once the catalogue L10 life is exceeded or after overload events
- 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
- smearing of rollers and journal during idle periods because the radial section holds too little lubricant
Selection pitfalls — read before you substitute
- On a 15 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 21 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- Oscillating pivots fail differently: rocking through a small angle concentrates wear in the same roller positions — inspect those zones, and consider rotating the assembly's clock position at service intervals.
- Contamination, not fatigue, kills most small needle bearings: with raceways this narrow, one hard particle dents a full-width line — seal the housing even when the bearing execution itself is open.
- The 18.7/24.5 kN ratings and 17 g mass are SKF catalogue values transcribed from ch. 7.1 of PUB BU/P1 17000 (PDF table page 616); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
What are the dimensions and ratings of the K 15x21x21?
A K 15x21x21 measures 15 mm bore/Fw × 21 mm outside diameter × 21 mm width (0.591 × 0.827 × 0.827 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 18.7 kN, static C0 24.5 kN, fatigue limit Pu 3 kN, limiting speed 26,000 r/min, reference speed 24,000 r/min, mass about 17 g.
How is the K 15x21x21 designation read?
K = needle roller and cage assembly (DIN 5402); the three figures give Fw 15 mm (shaft journal), E 21 mm (complement outside diameter, matched by the housing bore) and B 21 mm width. TN marks the glass fibre reinforced PA66 cage.
Can the K 15x21x21 run on an unhardened shaft?
No. In this execution the 15 mm shaft journal is the inner raceway: it must be ground and hardened to 58–64 HRC (with matching housing bore quality on the outside). If the shaft cannot meet that, order the inner-ring sibling (NKI/NA execution) plus its ground inner ring instead.
How should the K 15x21x21 be mounted?
Slide the assembly over the ground 15 mm journal with a mounting sleeve, bore the housing to E 21 mm, and retain with a washer spanning the cage. Never press against the cage or rotate before the bearing is lubricated and loaded.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.1 needle roller and cage assemblies on 2026-09-26. Read our editorial & correction policy.