One-way bearing clutches: HF, HFL and CSK sizes, operation and selection
A one-way bearing clutch transmits torque in one relative direction and overruns in the other. It is not simply a normal bearing that happens to turn more easily one way. Identify the locking mechanism, required support bearings, exact shaft and housing interface, torque duty and overrunning speeds before selecting a replacement.
On this page17 sections ⌄
How a one-way bearing works
In a roller-ramp clutch, relative motion in the driving direction wedges rollers into a narrowing space so that torque can pass between the members. Reverse relative motion releases that wedging action. A sprag clutch uses shaped locking elements that tilt between engagement and release rather than ordinary cylindrical rollers on ramps.
An indexing clutch turns repeated input movements into incremental rotation. An overrunning clutch allows one member to run ahead of the drive. A backstop prevents reverse movement in its intended arrangement. These functions require different duty checks even when a component looks similar.
A ball bearing, needle bearing and one-way clutch are not equivalent labels. Some assemblies include rolling support bearings as well as the torque-locking elements. A toothed ratchet with pawls is another mechanism and should not be substituted on the basis that both prevent reverse motion.
HF vs HFL vs CSK: what changes
A part sold as a “one-way ball bearing” may mean a supported sprag freewheel such as CSK, not balls acting as the locking elements. Obtain the actual manufacturer series before comparing capacities.
On smaller screens, scroll the table sideways to read all columns.
| Family / construction | Torque and support function | Selection consequence |
|---|---|---|
| INA HF drawn-cup roller clutch | Clutch without integrated support bearing arrangement | Provide the specified separate bearing support and suitable shaft raceway; HF is not an ordinary HK radial bearing |
| INA HFL drawn-cup clutch assembly | Clutch with integrated plain or rolling support arrangement | Check the exact support/load limits and longer envelope; do not assume a same-bore HF drops into its place |
| Stieber CSK | Sprag freewheel integrated with a ball-bearing support arrangement | The base series uses its specified press fits and initial clearance; check both torque and bearing loads |
| Stieber CSK..P / CSK..PP | Keyed variants of the combined freewheel | P has an inner keyway; PP has inner and outer keyways, with different recommended fits |
INA HF and HFL size, torque and speed reference
Exact existing Schaeffler medias records imported on 2 September 2026. Fw is the under-roller/shaft interface diameter; D and C are outside diameter and outer-ring width. These are named product records, not a universal one-way bearing size decoder.
Keep the two speed columns separate. For example, HF0812 has a rotating-shaft limit of 17,000 1/min and a rotating-outer-ring limit of 12,000 1/min in this record. Selecting only the larger number would lose the operating configuration.
HF0612 is 6×10×12 mm and HF0812 is 8×12×12 mm. A 12 mm shaft search concerns Fw, not the 12 mm outside diameter or width of HF0812. Compare all dimensions and the support arrangement before considering HF1216 or HFL1226.
Permissible torque in N·m is not a radial dynamic load rating in N or kN. It cannot be inserted as C in a rolling-bearing life calculation. The table does not determine a press fit, a shaft hardness requirement or suitability for a particular starter, reel or vehicle.
On smaller screens, scroll the table sideways to read all columns.
| INA model | Fw | D | C | Permissible torque | Rotating shaft limit | Rotating outer-ring limit |
|---|---|---|---|---|---|---|
| HF0612 | 6 mm | 10 mm | 12 mm | 1.76 Nm | 23,000 1/min | 13,000 1/min |
| HF0812 | 8 mm | 12 mm | 12 mm | 3.15 Nm | 17,000 1/min | 12,000 1/min |
| HF1012 | 10 mm | 14 mm | 12 mm | 5.3 Nm | 14,000 1/min | 11,000 1/min |
| HF1216 | 12 mm | 18 mm | 16 mm | 12.2 Nm | 11,000 1/min | 8,000 1/min |
| HFL0615 | 6 mm | 10 mm | 15 mm | 1.76 Nm | 23,000 1/min | 13,000 1/min |
| HFL0822 | 8 mm | 12 mm | 22 mm | 3.15 Nm | 17,000 1/min | 12,000 1/min |
| HFL1022 | 10 mm | 14 mm | 22 mm | 5.3 Nm | 14,000 1/min | 11,000 1/min |
| HFL1226 | 12 mm | 18 mm | 26 mm | 12.2 Nm | 11,000 1/min | 8,000 1/min |
Stieber CSK..P keyed freewheel reference
Selected CSK..P rows from Stieber catalogue MCC-P-7426-SC-EN-A4, May 2025, page 17. TKN is catalogue nominal torque; nmax is the listed maximum speed, not an approval for every duty cycle.
These rows apply to the P variant, not every CSK suffix. For example, the same table gives CSK12P-2RS a 14 mm width, compared with 10 mm for CSK12P. Do not apply a blanket “add 5 mm” rule to every sealed size.
Sizing still needs the manufacturer’s duty and mounting checks. Neither nominal torque nor a published maximum speed on its own establishes a permissible shock load, safety factor or machine holding capacity.
On smaller screens, scroll the table sideways to read all columns.
| Model | d mm | D mm | L mm | TKN N·m | nmax min−1 |
|---|---|---|---|---|---|
| CSK12P | 12 | 32 | 10 | 9.3 | 10000 |
| CSK15P | 15 | 35 | 11 | 17 | 8400 |
| CSK17P | 17 | 40 | 12 | 30 | 7350 |
| CSK20P | 20 | 47 | 14 | 50 | 6000 |
| CSK25P | 25 | 52 | 15 | 85 | 5200 |
| CSK30P | 30 | 62 | 16 | 138 | 4200 |
| CSK35P | 35 | 72 | 17 | 175 | 3600 |
| CSK40P | 40 | 80 | 22 | 325 | 3000 |
CSK..PP: two-keyway size reference
Stieber May 2025 catalogue, page 17. These are PP variants with keyways on both races. Dimensions b and t retain the outer-keyway drawing symbols; they are not replacement shaft dimensions.
A base CSK marking without P or PP remains a different variant. Similar envelope dimensions do not erase the keyway, mounting-fit and seal differences. Use the full drawing for fabrication.
On smaller screens, scroll the table sideways to read all columns.
| Model | d mm | D mm | L mm | TKN N·m | nmax min−1 | Outer b mm | Outer t mm |
|---|---|---|---|---|---|---|---|
| CSK15PP | 15 | 35 | 11 | 17 | 8400 | 2 | 0.6 |
| CSK17PP | 17 | 40 | 12 | 30 | 7350 | 2 | 1.0 |
| CSK20PP | 20 | 47 | 14 | 50 | 6000 | 3 | 1.5 |
| CSK25PP | 25 | 52 | 15 | 85 | 5200 | 6 | 2.0 |
| CSK30PP | 30 | 62 | 16 | 138 | 4200 | 6 | 2.0 |
| CSK35PP | 35 | 72 | 17 | 175 | 3600 | 8 | 2.5 |
| CSK40PP | 40 | 80 | 22 | 325 | 3000 | 10 | 3.0 |
Shaft, housing and keyways: suffixes change the fit
These are the cited Stieber series recommendations, not a generic fit for every one-way bearing. C5 here belongs to that supported freewheel design; it is not a reason to select C5 for an unrelated standard bearing.
A drawn-cup clutch acting on a shaft needs the manufacturer’s raceway geometry, finish and material requirements as well as its nominal size. A smooth-looking mild-steel shaft is not automatically a suitable hardened raceway. Do not fabricate a universal hardness or interference value from the bore diameter.
On smaller screens, scroll the table sideways to read all columns.
| Stieber variant | Shaft recommendation | Rigid housing recommendation | Important distinction |
|---|---|---|---|
| Base CSK | n6 | N6, steel | Torque transmission by specified press fits; the cited base design has initial C5 radial clearance |
| CSK..P | k6 with inner-race keyway | N6, steel | The keyway changes the shaft mounting requirement |
| CSK..PP | h6 with keyways | H6 with outer keyway | Both interfaces are keyed; this is not the base press-fit arrangement |
Grease, oil and temperature limits
The cited Schaeffler drawn-cup range is supplied greased as standard; ungreased versions are available for oil-lubricated arrangements. That does not make arbitrary grease or oil interchangeable. Retain the exact variant and the specified lubricant, quantity and supply method.
Stieber describes grease-filled CSK units and permits oil-bath arrangements under its instructions. For either ambient or operating conditions outside +5 to +60 °C, its cited guidance requires a suitability review. This range is not a claim that every one-way clutch shares the same thermal limit.
Do not wash out a sealed or prelubricated clutch and then choose lubricant by colour. Excess or unsuitable lubricant can change engagement and overrunning behaviour. Lubrication guidance for a ball bearing alone does not automatically cover a sprag or roller-locking mechanism.
One-way bearing slipping, locking both ways or not releasing
Secure stored and suspended loads before inspecting a backstop or drive. Do not deliberately release a loaded backstop to see whether it works. High-consequence holding duties require the equipment-specific safety arrangement, not a hand-spin diagnosis.
On smaller screens, scroll the table sideways to read all columns.
| Observed symptom | Check without assuming a cause | Next decision |
|---|---|---|
| Slips in the intended drive direction | Actual relative locking direction, full part identity, worn mating raceway, contamination, lubrication and applied torque | An unloaded hand check cannot establish capacity; follow the equipment load-test and replacement criteria |
| Locks or drags in both directions | Distorted fit, damaged parts, misalignment, inadequate support or unsuitable lubrication | Stop operation and inspect the complete support and clutch system |
| Intermittent engagement | Surface damage, wear, contamination and duty conditions | Do not treat a temporary solvent clean as proof that the clutch is serviceable |
| Heat during overrunning | Which race overruns, its actual speed, support loads and lubricant | Use the correct speed limit, not the larger of two catalogue numbers |
| Replacement appears to lock backwards | Viewing direction, input/output assignment and part orientation | Clockwise without a defined viewpoint is ambiguous; confirm against the equipment drawing |
Starter, ATV, motorcycle, RC and reel searches
A device-specific query needs the exact equipment model, year or revision, original part number, mating races, drive direction and assembly drawing. A generic HF or CSK dimensions table cannot establish compatibility with a Yamaha, Honda, Can-Am, Royal Enfield, Traxxas, HPI or fishing-reel assembly.
BearingScope separates a possible dimensional candidate from a verified replacement. Where the OEM correspondence is unavailable, the fitment remains unverified. A one-way linear bearing query also needs a separate linear mechanism reference; this rotary clutch guide does not answer it.
One-way clutch questions
Can a normal bearing replace a one-way bearing?
No. Ordinary radial support does not provide the required directional torque-locking function. A combined freewheel can have ball-bearing support and a separate locking mechanism in the same assembly.
What is the difference between HF0812 and HFL0822?
Both have an 8 mm shaft interface in the listed INA records, but HF is a clutch requiring separate support and HFL includes a support arrangement. Compare the complete dimensions and load requirements; they are not automatically interchangeable.
Which one-way bearing is best?
Select by the exact torque duty, overrunning member and speed, support loads, environment and mounting interface. A larger bore or higher headline torque is not a complete selection.
Can I repair a slipping starter clutch by adding grease?
Not as a general remedy. The exact starter assembly, mating races, wear criteria and specified lubricant must be checked. This guide does not certify an equipment repair.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Mechanism | Roller ramp, sprag or another clutch design | Do not infer the mechanism from the word bearing. |
| Support | Separate support bearings or an integrated arrangement | HF and HFL serve different support requirements. |
| Direction and duty | Locking direction, overrunning member, starts and peak torque | An unloaded hand test is not a rated torque test. |
| Exact identity | Full designation, interfaces and equipment reference | A matching bore does not establish OEM fitment. |
A practical investigation sequence
Identify and record
Record the exact clutch marking and machine function: indexing, overrunning or backstopping. Record which member rotates and define the viewing direction used for clockwise or anticlockwise descriptions.
Check the context
Measure the shaft interface, outside diameter and axial envelope, and identify the support bearing arrangement. Keep the clutch, keys, sleeves and any separate support bearings distinct.
Verify before acting
Check torque duty, shocks, engagement frequency, each overrunning speed, lubrication and temperature against the exact manufacturer selection instructions. Confirm shaft and housing material, tolerance and retention.
Keep the decision traceable
Use the equipment procedure for safe isolation, installation and direction verification. Restore guards and test under the specified commissioning conditions; stop if the clutch slips, binds, overheats or fails to release.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- Schaeffler medias: drawn-cup roller clutch construction and support arrangements — Manufacturer-specific factual reference. Edition, test conditions, exact series and selection limits retained; not a universal equipment approval.
- Stieber: CSK and CSK..2RS freewheels, mounting and operating conditions — Manufacturer-specific factual reference. Edition, test conditions, exact series and selection limits retained; not a universal equipment approval.
- Stieber MCC-P-7426-SC-EN-A4, May 2025, CSK..P / CSK..PP / CSK..P-2RS, pages 16–17 — Manufacturer-specific factual reference. Edition, test conditions, exact series and selection limits retained; not a universal equipment approval.
- Schaeffler medias INA HF0612 product 407310; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HF0812 product 407312; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HF1012 product 407314; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HF1216 product 407316; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HFL0615 product 407399; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HFL0822 product 407401; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HFL1022 product 407403; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
- Schaeffler medias INA HFL1226 product 407406; imported 2026-09-02 02:05:39 — Exact manufacturer product record: Fw, D, C, permissible torque and separately identified rotating-shaft / rotating-outer-ring speed limits.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.