Abstract: A rotor assembly for a stepping motor is provided by locating one flat side of a brittle annular rotor disc against an annular alignment surface on a hub and mounting the hub with aligned rotor disc thereon on a central shaft carrying an annular clamping washer. The clamping washer includes an inner peripheral portion which is clamped between first and second abutment surfaces on the shaft and hub and a resilient outer peripheral portion which bears axially against the other flat side of the rotor disc with a spring-like bias to clamp the disc in prealigned position on the hub. Required alignment of the brittle rotor disc is thereby achieved while minimizing the danger of breakage and also reducing the number of rotor components and assembly steps.