Best quality red rubber. Shore hardness in range 46-55. Bottom diameter moulded on top face. Resistant to dilute acids alkalis and ammonia.Bottom Diameter: 23mmTop Diameter: 26.5mmLength: 28mmTemperature Range: -30°C - 70°CPack of 10Size 23 stoppers are ideal to use with Pyrex Heavy Wall Filter Flasks 100mL and Simax WM flasks 100mL.