The Hyrax® RPE "Click" Expander has a patented "Click" feature to prevent unwanted reversing for rapid palatal expansion in the fixed appliance. When the Hyrax® RPE "Click" Expander is properly activated by ¼ turn, both the patient and doctor will be able to feel the screw “lock”. The hole in the spindle is always in the correct position for reactivation/turning. By chance if the Hyrax® RPE "Click" Expander is overactivated, it can be turned back.