Unit comprising at least two torsion bars for limiting the force in a belt retractor

A unit comprising at least a first and a second torsion bar for limiting the force in a belt retractor, said first torsion bar being hollow and said second torsion bar being arranged in the interior of said first torsion bar, said first torsion bar having an inner diameter which is at least in part selected such that said first torsion bar is supported at least in a twisted condition by said second torsion bar, a torque which can be transmitted as a maximum by said first torsion bar differing from a torque which can be transmitted as a maximum by said second torsion bar, one of said first and second torsion bars being dimensioned such that with increasing loading it shears off so that only the remaining of said first and second torsion bars is involved in transmitting the torque.