These were developed to keep the vegetables below the level of the liquid in the jar, which is really about the only cause of possible failure when using lacto fermenting preserving methods. They are made of non iridized glass. Glass is known to be one of the most inert substances and should not leach chemicals into your Ferment. These fermenting weights are not meant to be heated in any way. Size 2 3/4” wide and about 2/3″ thick to fit a wide mouth canning jar.