A Mason jar — named after John Landis Mason, who patented it in 1858 — is a molded glass jar used in home canning to preserve food. The jar's mouth has a screw thread on its outer perimeter to accept a metal ring or "band". The band, when screwed down, presses a separate stamped steel disc-shaped lid against the jar's rim. An integral rubber ring on the underside of the lid creates a hermetic seal. The bands and lids usually come with new jars, but they are also sold separately. While the bands are reusable, the lids are intended for single-use when canning. Glass jars and metal lids are still commonly used in home canning while they have been largely supplanted by other methods for commercial canning (such as tin cans and plastic containers).
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