materials: arilock grommet is made of durable silicone and PBA which is durable and resistant to high temperatures for long-term use Good performance: this fermenter lid grommet is easy to install into the lid and hermetically sealed to food from oxygen; You can use this product with airlocks to keep the fermentation for a period of time Hermetic sealing: this silicone grommet is combined with the airlock and has a good hermetic seal to prevent oxygen from entering the fermenter; This helps to keep the enzyme fermented for a long time and size: you will 50 arilock grommet with an outer diameter of 5/8 inches and an inner diameter of 3/8 inches; You need to drill a 5/8 inches hole in the fermenter lid; Then the airlock grommet is very easy to insert cover hole Wide use: this airlock gasket is suitable for any type of airlock and plastic lid and straw; Use these silicone gaskets to convert jars into airlock fermentation vessels Features:Made of durable and long lasting silicone, the airlock grommet with good hermetical sealing performance fits airlock and you can use the airlock grommet to turn jars into drinking bottles. Various application: This airlock grommet fits with types of airlocks and plastic buckets and straws. It is much convenient for you to make your own airlock for fermenting with useful product. Easy installation into a bucket lid and provides a good sealing. Specification: Colour:black Material:rubber Size:Outer diameter: 1.59cm Package Contents: 50 * Exhaust valve gasket Only the above package content, other are not included. Note: Light and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.