Use Thermo Scientific™ SureSTART™ 18 mm Precision Screw Caps with screw vials that have an 18 mm opening, including our SureSTART 10 mL and 20 mL Screw Top Headspace Vials (Level 3). Select Level 3 products for ultimate performance and sensitivity from your methods, while maintaining the highest levels of sample security and integrity. Choose from magnetic steel caps with all-purpose silicone/PTFE septa designed to reduce autosampler needle issues. Select High Temperature septa to allow for heating to over 250°C without excessive septum softening or the release of volatile vapors.