HK1212FM bearing: complete specifications & equivalents
The HK1212FM is a ISO 3245 radial bearing sized 12 x 18 x 12 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 12 mm |
| Outer diameter D | 18 mm |
| Width B | 12 mm |
| Seal / shield | open |
| Basic dynamic load rating C | 6.6 kN |
| Basic static load rating C0 | 7.3 kN |
| Fatigue load limit Pu | 0.89 kN |
| Limiting speed (mechanical) | 13000 rpm |
| Mass | 9 g |
| Manufacturer designation | HK1212FM |
| Standard | ISO 3245 |
| Catalog version | CAT. No. 2203-3/E 2024 |
| Last verified | 2026-09-25 |
Source: catalog reference (CAT. No. 2203-3/E 2024) · extracted 2026-09-25
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (CAT. No. 2203-3/E 2024); 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 & HK-series range
| Bore d | 0.472 in |
|---|---|
| Outer diameter D | 0.709 in |
| Width B | 0.472 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 3 mm |
| Smallest bore in HK-series | 3 mm |
| Largest outer diameter in HK-series | 58 mm |
| Width range across HK-series | 6–38 mm |
| Bore position in HK-series (smallest first) | 9 of 24 |
| Bore above smallest HK-series size | 9 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the HK1212FM model number is decoded
NTN HK1212FM belongs to the HK-series of open-end drawn-cup needle roller bearings (ISO 3245).Fw = 12 mm names the shaft journal that doubles as the inner raceway; around it the drawn cup measures 18 mm outside and 12 mm across. There is no separate inner ring — the thin-walled cup is drawn from sheet steel, hardened, and press-fitted into the housing, giving the smallest radial section of any rolling bearing at this shaft size. The FM/FT2 suffix marks NTN's caged drawn-cup execution: a formed steel cage keeps the rollers evenly spaced, lowering friction and noise versus full-complement drawn cups. This is the classic two-wheeler and small-engine size class: the cup replaces a bulky machined bearing and lets the gearbox casing shrink around it. This size is frequently specified in motorcycle gear-selector mechanisms, where the shaft is short, the housing is cast around the bearing, and the roller set must survive repeated shock from shift forks. Grease for this size should be a soft NLGI 1 or 2 lithium-complex grade: the open cup lets the housing supply the lubricant, and a stiff grease will not flow back through the roller set after standstill.
Typical equipment & failure modes
Common applications
- small hydraulic pump drives
- automotive accessory drives
- lawn and garden equipment spindles
- dirty environments where the open ends rely entirely on the housing seals
Known failure patterns
- fretting of the cup outer surface in a soft or worn housing seat
- scoring of the needle rollers from abrasive contamination past the open ends
- brinelling of the drawn cup from hammer blows during press-in mounting
Selection pitfalls — read before you substitute
- The cage in HK1212FM spaces the rollers but is not a seal: it retains nothing against dust or washdown, so the housing still needs its own sealing arrangement at 12 mm.
- The 12 mm standard width of HK1212FM is the general-purpose section at 12 mm shaft; wider HK variants in the same 12×18 mm envelope carry more load and are not interchangeable if the housing width is fixed.
- Press the drawn cup in with a mandrel bearing on the stamped face only — never hammer the cup or press through the rollers, that cracks or brinells the shell.
- With no inner ring, HK1212FM reads the 12 mm shaft surface as its raceway: hardness 58–64 HRC and a ground finish are prerequisites, not recommendations.
Frequently asked questions
What does Fw mean on a HK1212FM drawn-cup bearing?
Fw is the under-roller diameter — the diameter of the shaft journal on which the needle rollers run directly. For HK1212FM, Fw = 12 mm, so the shaft must be machined to 12 mm, hardened to 58–64 HRC and ground, unless a separate IR inner ring is fitted.
Can a HK1212FM needle roller bearing carry axial load?
No. Drawn-cup needle roller bearings like HK1212FM carry radial load only and provide no axial shaft location. Axial forces must be carried by separate thrust washers or a locating bearing in the arrangement.
Does HK1212FM need a hardened shaft?
Either the 12 mm shaft journal must be hardened to 58–64 HRC and ground to Ra ≤ 0.2 µm, or you can fit the matching inner ring (IR8x12x12.5) so a standard unhardened shaft can be used.
What are the dimensions of a HK1212FM needle roller bearing?
A HK1212FM drawn-cup needle roller bearing has a 12 mm shaft diameter (Fw, under-roller diameter), 18 mm outside diameter and 12 mm width, per ISO 3245 boundary dimensions. It has no inner ring — the shaft journal serves as the raceway.
Reviewed & verified by the MPN Base engineering desk against source catalog CAT. No. 2203-3/E 2024 on 2026-09-25. Read our editorial & correction policy.