The Frelan Hardware 100mm Ball Bearing Butt Hinge Black is suitable for internal residential doors 40-44mm thick.  A pair of hinges is adequate; however, we would always suggest fitting 3 hinges per door as this will look more aesthetically pleasing to the eye.  From a practical point of view the use of 3 hinges will help to overcome twisting or warping which sometimes happens to doors over a period of time where heat and moisture are a factor, for instance bathroom and airing cupboard doors. Ball bearing hinges have always been very popular for their smooth operation, durability, l...