The instant invention relates to a process and plant for the transformation of dangerous wastes containing chromium six as contaminant into non dangerous wastes that can be stored without special care and will be degraded in the environment without time limit. The locking member includes a key portion for unlocking the tightening mechanism when the cable is removed from the item. Swing pawl members each disengageably engage projections formed at circumferentially spaced positions on the inner peripheral surface of each driven gear n to control engagement and disengagement between each driven gear n and the driven gear shaft.