The rotation of disk 1, keyed on driving shaft A, is transmitted through balls 2 to driven shaft B. Balls 2 enter recesses in disk 3 which is keyed on shaft B. When the torque applied to shaft B exceeds the permissible value, balls 2 overcome the resistance of springs 4 and are forced out of the recesses of disk 3. This stops the transmission of rotation from shaft A to shaft B.
$2189$WL,C$