Wheaton headspace vials accept 20 mm aluminum seals Rounded shoulders and bottoms, allowing for even heating and safer operation at higher pressures Manufactured from Type I borosilicate glass Top provides a tighter seal with your septa O.D. x Height: 23 x 75 mm Capacity: 20 mL. 20 mm Crimp Top Aluminum Silver Cap with PTFE/Silicone Septa.