These lid discs are made for use with Kilner screw-top preserve jars and screw bands. Their built-in rubber rim creates a vacuum seal for safely processing foods in a boiling-water bath, so your homemade preserves stay airtight and fresh. Set of 12 lid seals. 2 5/8" diam.; fits 1-pint and 1-quart jars. A good vacuum seal has been achieved when the lid is pulled down toward the food in the jar, creating a dip in the lid. Dating back to 1840s England, Kilner is a leading European name in food preserving.