Abstract: A pneumatic spring having a cylinder piston and piston rod biased toward extended condition by compressed gas in the cylinder, an elongated cover tube severed at one of its ends to the outer end of the rod, extending over the length of the rod to define an annular space therebetween, and always in axial alignment with and extending over portions of the cylinder. A transversely shiftable plunger lock assembly on the cover tube near its open end includes a fixed body and a lock plunger movable transversely of the piston axis into the annular space when the rod and cylinder are extended, to abut the annular end of the cylinder to securely retain the assembly in one position, preferably a substantially extended condition.