Conversion. Beverage containers to aviation oxygen cylinders. After the circumferential straps are welded to the cylindrical portion, in the metal division of a large Eastern rubber factory, rough edges and accumulated weld scale are removed by a skilled workman. The twin rotary brushes, shown above, do their work on the inside and outside of the cylinder in the same operation. This process is required in the manufacture of shatterproof oxygen cylinders for high altitude flying. Firestone, Akron, Ohio. Sourced from the Library of Congress.