Shiny Metal One Piece Storage Lids Caps for Mason Jars (12 Pack, Regular Mouth) 12 Leak Proof Metal Storage Caps for *Regular Mouth* (2 3/8" Internal Diameter) Mason Jars. Made in the USA! We love these lids for fridge, freezer, and dry goods storage! They are also great for all types of crafts, candles, and storage. If you use Mason jars for drinking or storage, it is essential to have an adequate supply of one piece lids. Two piece lids seal equally well but they are cumbersome to repeatedly take on and off the jar. These serve a similar function to the plastic Ball storage lids but are more durable, seal better, and look nicer. The plastic ones tend to crack and break, especially if the jar gets dropped or tipped over. They can be used for hot fill products, but not for water bath canning. They are made of tin plated steel with a plastisol liner. We use them a lot for capping unfinished drinks, leftover food, fermented food, and sauces in the fridge. Our kids drink out of half pint jars, so when they dont finish their drink we just put a lid on it and put it back in the fridge. In the pantry we use them on nuts and seeds, flour, sugar, and other staples.