An extension assembly is connected or connectable, in terms of driving, to a double-motor rheometer. The double-motor rheometer includes first and second measuring motors controllable independently of each other, and provided for determining a torsional moment generated by the corresponding measuring motor. The extension assembly includes first and second sample holding parts for holding a first sample portion and a second sample portion of the sample. The first sample holding part is driveable by the first measuring motor in a rotational movement about a first axis, and the second sample holding part is driveable by the second measuring motor in a rotational movement about a second axis. The first axis is arranged so as to be parallel to and spaced apart from the second axis. The sample held in the first sample portion and in the second sample portion extends between the respective sample holding parts.