Before selecting a one way clutch bearing, buyers should check five facts: required torque, maximum overrunning speed, shaft bore and housing tolerance, the duty the clutch performs (overrunning, indexing or backstopping), and lubrication plus rotation direction. These five determine whether the clutch locks reliably, runs cool and lasts. Bore size alone is never enough. Use this checklist so a low-cost part never stops a production line.
A clutch that fits the shaft but is under-rated will slip under load, overheat during overrunning, or wear out within weeks. Because a one way clutch is a locking element, a wrong choice can even cause sudden reverse rotation on a conveyor. Checking five parameters takes minutes and prevents unplanned downtime that costs far more than the part.
A sprag clutch is a cage of small, precisely angled sprags running between an inner and an outer race. Turning one way, the sprags tilt and jam, locking the races together so torque is transmitted; turning the other way, they release and freewheel. SUMA DC series cages are GCr15 bearing steel at HRC 60–62 surface hardness (0.6 mm minimum) with HRC 35–45 cores, supplied without races so the customer's shaft and housing become the raceways.
| Parameter | Why It Matters | Buyer Should Check |
|---|---|---|
| Torque Capacity (TKN) | Sets the load the clutch transmits before slipping; peak torque is about 2 × TKN. | Required drive torque, shock load and safety factor. |
| Overrunning Speed | Too high a freewheel speed causes sprag lift, heat and wear. | Inner-race (nimax) vs outer-race (namax) speed. |
| Bore Size & Shaft Fit | Wrong fit causes slip or seizure and uneven sprag loading. | Shaft tolerance and race hardness (HRC 60–62). |
| Width / Sprag Space | Determines axial space and the minimum race plain width. | Housing width and race plain width. |
| Application Mode | Overrunning, indexing and backstopping load the clutch differently. | Which duty the clutch performs. |
| Lubrication | Prevents wear and heat; the wrong lubricant affects lock-up. | Oil or grease recommended for the version. |
| Rotation Direction | A one way clutch locks in one direction only. | Machine rotation and mounting orientation. |
| Item to Check | Why It Matters | What to Supply |
|---|---|---|
| Torque | Prevents slip under load. | Drive torque and safety factor. |
| Overrunning Speed | Prevents heat and wear. | Max rpm of the freewheeling race. |
| Bore & Tolerance | Correct fit transfers torque. | Shaft diameter and tolerance. |
| Duty | Defines the clutch type. | Overrunning, indexing or backstopping. |
| Lubrication & Sealing | Long life at temperature. | Oil or grease and environment. |
| Rotation Direction | Correct lock-up. | Machine rotation sense. |
The three duties are not interchangeable. Overrunning freewheels in one direction and locks in the other, so its overrunning speed limit governs the choice. Indexing produces accurate intermittent motion and is limited mainly by torque and indexing accuracy. Backstopping only holds against reverse rotation, so holding torque matters most and freewheel speed is low. Choosing the wrong duty is one of the most common causes of premature clutch failure.
Q1: Is bore size enough to select a clutch?
A: No. Torque, speed and duty decide capability and type.
Q2: How much torque margin should I add?
A: Allow for shock, since peak torque is about 2 × TKN.
Q3: Do I need to harden the shaft?
A: Yes, the race should reach HRC 60–62 for correct operation.
Q4: What is the easiest mistake to avoid?
A: Choosing by bore alone without checking torque and overrunning speed.
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