The invention concerns a grinding head for a mobile grinding machine which is suitable for grinding floor surfaces, and a mobile grinding machine comprising such a grinding head. The grinding machine is driven by a motor and has a rotatable planet disc and grinding heads (5-7) rotatable relative to this. The grinding heads (5-7) comprise a carrier (8) which is designed to be rotated by means of the motor, and a grinding disc (9) designed to be driven by the carrier (8) by means of a coupling element (10). The coupling element (10) comprises a multiplicity of plates (11-13) which are stacked on each other, each with a central opening (14) and drain holes (15) distributed around this, and a compression spring (16) which extends through the central opening (14) of the plates (11-13) and by means of screw elements (17) is clamped between the carrier (8) and the grinding disc (9). The screw elements (17) extend through the drain holes (15) of the plates (11-13) and are arranged to connect, alternately in a circular direction around the central opening (14) of the plates (11-13), the carrier (8) with the plate (13) nearest the grinding disc (9) and the grinding disc (9) with the plate (11) nearest the carrier (8). A coupling element is also shown for a mobile grinding machine for grinding a stone floor.