When the active and inactive leafs are open, the co-ordinator arm pivots downward, positioning the arm and rubber roller below the top of the active leaf. As the active leaf is closed it comes into contact with the arm and roller and is held open. When the inactive leaf is closed, the nylon roller on the co-ordinator mechanism comes into contact with the roller strike and lifts the projecting arm above the top of the active leaf, allowing it to close in the correct sequence. When the active leaf is in the closed position, the door bracket on the inactive leaf and the nylon roller position the co-ordinator arm above the top of the leaf allowing it to open and close freely. ALTHOUGH THIS PRODUCT IS UL LISTED IN THE USA, IT IS NOT CE MARKED, DOES NOT HAVE A DoP AND SHOULD NOT BE USED ON FIRE RATED DOORS.