GREASE AND OIL RETAINERS OF THE FRICTION TYPE USED TO SEAL THE SPACE BETWEEN A HOUSING AND A ROTATING OR RECIPROCATING SHAFT, [ OR THE SPACE BETWEEN A PISTON AND CYLINDER WALL- ]NAMELY, RETAINERS MADE OF UNITARY CIRCULAR RINGS OF FELT, LEATHER, OR COMPOSITION; RETAINERS MADE OF UNITARY CIRCULAR RINGS OF FELT, LEATHER, OR COMPOSITION, AND HAVING A SPRING FITTED THERETO; RETAINERS MADE OF UNITARY CIRCULAR RINGS OF FELT, LEATHER OR COMPOSITION, HAVING A SPRING FITTED THERETO, AND THE WHOLE HELD WITHIN A CAGE OR SHELL OF DUCTILE STEEL, BRASS, OR ALUMINUM