UK'S MOST POPULAR LOW-COST METHOD OF CLOSING A FIRE DOOR (OR NORMAL DOOR). RECOMMENDED FOR INTERNAL DOORS, THEY ARE FITTED INTO THE DOOR EDGE, WITH THE CHAIN PLATE ATTACHED TO THE FRAME. WHEN THE DOOR IS OPENED, THE SPRING RECOILS AND FORCES THE DOOR TO SHUT. CHAIN TENSION CAN BE ADJUSTED ALLOWING A GOOD DEGREE OF FLEXIBILITY IN SETTING THE DOOR CLOSING RATE.