Made of food-safe grade silicone, environmental-friendly and non-toxic Able to be sterilized at very high temperature over 100 Degrees Celsius due to its silicone material feature Perfect acid, alkari and corrosion resistant, better than any other rubber or plastic stoppers Ideal for laboratory, household, and industrial use, various demensions to prevent oxygen from wreaking havoc with your fermenting process Smooth and tapered sides designed for exceptional sealing and optimal fit with a wide range of openings, easy to plug in or pull out, creating an airtight seal Specification: Please note that the "20-25mm" is referring to the appliacable glass container' opening diameter range. For example, 20-25mm stopper adapts to the wine bottles' opening of 20mm to 25mm diameter. The specifcs of stopper itself can be checked below. 20-25mm: Height: 42mm/ 1.7inch; Top diameter: 25mm/ 1.0inch; Bottom diameter: 20mm/ 0.8inch 24-30mm: Height: 49mm/ 1.9inch; Top diameter: 30mm/ 1.2inch; Bottom diameter: 24mm/ 0.9inch 27-32mm: Height: 46mm/ 1.8inch; Top diameter: 32mm/ 1.3inch; Bottom diameter: 27mm/ 1.1inch 29-35mm: Height: 47mm/ 1.9inch; Top diameter: 35mm/ 1.4inch; Bottom diameter: 29mm/ 1.2inch 33-38mm: Height: 52mm/ 2.0inch; Top diameter: 38mm/ 1.5inch; Bottom diameter: 33mm/ 1.3inch Package Includes: 1 piece glassware stopper(3 Pack) Note: Please allow 1-2 mm inaccuracy due to manual measurement. Thanks.