The invention relates to a replaceable adaptor for attaching a headset device to a helmet, which comprises: (a) a lower portion at a lower level having a shape suitable to be accommodated within a helmet cavity at the helmet; and (b) an adaptor cavity which is adapted to accommodate said headset device; wherein when a need is arisen to attach another headset having a different shape or dimensions to a same helmet, or when a need is arisen to replace the helmet by another helmet having a cavity of different shape or dimensions, said adaptor is replaced accordingly.