These metal SNAP lids and screw bands for mason jars seal home canned foods airtight. After heat processing and upon cooling, a vacuum is formed which seals the lids onto the jars. The lids are laquered to prevent rust and have an interior enamel coating to resist natural food acidity. Pack of 12 lids and 12 screw bands Size: Standard mouth (70 mm) Colour/Pattern: Silver-tone Dimensions: 70 mm Dia Screw bands can be reused, but SNAP lids are designed for one-time use only.~For best results, fill hot jar with prepared recipes, leaving recommended headspace. Wipe jar rim and threads with a clean, damp cloth removing any stickiness. Center hot SNAP lid on jar. Apply screw band just until fingertip tight; do not overtighten. After processing, remove jars from canner and set upright on a towel in a draft-free place. Do not retighten screw bands or check for seal while jars are hot. Cool processed jars upright, undisturbed for 24 hours. After 24 hours, check seals. Sealed lids curve downward and do not move when pressed. (Any unsealed jars should be reprocessed or refrigerated.) For all sealed jars, remove screw bands; wipe and dry bands and jars. Store screw bands separately or replace loosely on jars, as desired.