Abstract: A pneumatic spring of the piston-and-cylinder type suitable for balancing the trunk lid of a motorcar and like applications is equipped with a stop mechanism which stops relative axial movement of the piston or piston rod and of the cylinder in response to a force axially applied to the spring, but releases the cylinder and piston or piston rod from each other in response to an applied force greater than the first-mentioned force. Cooperating stop members on the cylinder and piston rod engage each other as long as the relative axial movement of the principal spring elements is stopped.