Steel-saving glass-top jars recommended by the War Production Board, Containers Division, for home canning of the Victory garden fruits and vegetables in 1943. Third step is to allow expanding air inside the jar to escape during the processing; the screw band should be turned as far as it will go and then turned back about a quarter turn. Immediately after processing. the screw band must be made as tight as possible to ensure a perfect seal. The jar is then set aside in an upright position to cool