to seal against liquid leaking out around a rod which is slidably movable lengthwise axially within a chamber containing the liquid through an opening in the rear wall of the chamber , a ring of thermoplastic material is placed in the chamber around the rod and pressed against the rear wall of the chamber while applying heat to cause the thermoplastic material to flow into the opening around the rod and onto the outside of the wall so that when the heat is removed the material sets and latches itself onto the rear wall to seal off the space around the rod while still allowing the rod to slide easily .