112 are urged by the compressed spring into reciprocal indents 114 disposed on the secondary planet ring 70 when the indents are aligned with the balls the application of a torque force to the secondary planet ring which force exceeds the urging force applied by the spring to the balls via the thrust plate causes the secondary planet ring to rotate with respect to the gearbox the balls are forced out of the indents and the balls roll along side face of the secondary planet ring until they engage with another indent this process repeats itself until the torque force applied to the secondary planet ring is removed or until the force no longer exceeds the spring force whilst the secondary planet ring rotates no rotational movement is transferred to the second carrier stage 56 in this state that is when the clutch is overloaded the drive train is said to be stalling the spring force is adjusted by rotating the collar thus adjusting the compression of the spring in fig2 the spring is shown in its most compressed state thus requiring a relatively high torque to stall the drive train rotation of the collar so that the spring is more relaxed results a relatively low spring force being applied to the balls and hence a relatively low torque is required to stall the drive train it.