This special design feature applied to all the hinges of Lock & Lock products is one of its great secrets. By doing this a weld line does not form on the lid clips making them much easier to use and almost unbreakable. Testing conclusively shows you can open and close a Lock & Lock lid over 3 million times before it fails. Nearly every other product on the market suffers from broken clips, not Lock & Lock. This feature almost makes Lock & Lock lids incredibly easy to open and close. Great for st