A flexible shaft drive transmission coupled between a drive motor and a gear train of a power operated tool. The flexible shaft drive transmission includes: an outer casing having a bushing positioned at a tool end of the casing, the bushing defining a longitudinal central opening; lubricant disposed within the outer casing; and an elongated drive transmitting shaft assembly rotatable within the outer casing including a flexible drive transmitting and a coupler fitting affixed to the tool end of the drive transmitting shaft, the coupler fitting including a cylindrical body and an enlarged head extending distally from the cylindrical body, the cylindrical body fitting within the longitudinal central opening of the bushing and the enlarged head having a diameter greater than a diameter of the longitudinal central opening of the bushing. The enlarged head defining a square drive aligned with a central longitudinal axis of the drive transmitting shaft assembly.