<1>While the engine cranks
When the clutch gear (outer) revolves faster than the spline shaft (inner), the clutch rollers are forced to the narrower section, and so the revolving force of the clutch gear is transmitted to the spline shaft.
<2>After the engine starts
When the spline shaft (inner) revolves faster than the clutch gear (outer), the clutch rollers are forced to the wider section, causing the clutch gear to revolve idly.
If the one-way clutch that works as the overrunning clutch slips, the engine cannot be cranked even though the starter revolves.