These pneumatic cylinders are designed for a maximum operating temperature of 300 °C. They operate clamping devices that hold parts in place for a heat treatment process. To do this, the cylinders are extended, actuating the clamping device, and then depressurised. An internal safety catch holds the piston rod in the front end position. The cylinders are heated to 300 °C in the oven together with the clamping device and the workpieces. A sealing and lubrication system adapted to the temperatures ensures permanently safe operation