Grade 14 Concealed Bearing Triple Knuckle Hinge. Square (Max Load 160kg) They have a CE mark and are Certifire tested. BS EN 1935 rated. Comes with a 25 year mechanical guarantee and are fire door rated. Suitable for all domestic, commercial and industrial use. For standard internal residential doors a pair of hinges is adequate;Â however fitting 3 hinges per door has its advantages. It will look aesthetically pleasing and from a practical viewpoint it helps spread the load evenly and will help to overcome twisting or warping. This can sometimes happen to doors over a period of time where heat and moisture are a factor.