Microgreen grower for *wide mouth* Ball Mason jars, may fit some generic ones too. If planting smaller seeds, use paper towel, cotton cosmetic wipes, hydroponic grow mats, coir mats, etc to keep seeds in place. Check out my YouTube channel Keep on Growin' where I have videos on how to plant these. Microgreen growers are 2 3/4" diameter and 1 3/4". Note: All the wide mouth jars are slightly different, even the Ball Mason jars. The tops are flared so they work as long as they don't fall to the bottom. I made them that size so that they would fit in most jars. Some sit on the lip while some slide slightly inside. You may want to purchase a set of adjustment rings to hold the microgreen growers on the rim of the mason jars. Made out of PLA, plant based. *Hand wash warm soapy water only, not dishwasher safe. *Do not leave exposed to sunlight when not in use.