SMC Pneumatic Cylinder MDBBL50-400-RN-Z73 Spring Loaded Safety Lock 400mm StrokeSMC Pneumatic Cylinder MDBBL50 400 RN Z73 The spring loaded lock keeps the cylinder locked in the fully extended position until air is applied to retract the cylinder. The spring lock is overcome by the pressure to retract the cylinder, a neat feature for extending and holding a load in place without need for constant air pressure. Thanks for looking and feel free to ask questions! International buyers please note: Import duties, taxes, and charges