A. Put on screw bands firmly so that they are hand tight. If they are applied too tightly, the flat may buckle. If the flat buckles then the jar will not seal properly. If the band is too tight and doesn;t buckle, it may still not seal properly as it doesnt allow for the expansion that occurs during the process and thus will likely cause over flows as the food/liquid in the jars attempts to circulate. If you get liquid from foods between the rim of the jar and the lid the seal will likely be ineffective and fail after a few days or weeks.
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- John Lennon