Standard 20mm aluminum seal Headspace Vials with Flat Bottoms that form a tight seal with closure for accurate analysis and reproducible results. They are 

Clear 20 ml headspace vials designed to fit most headspace autosamplers.Designed to use separating organic and inorganic compounds for analysis, 

10/20mL Clear /Amber Precision Crimp Headspace Vial, Flat/Round Bottom, 22.5*46mm . 5).PTFE/Silicone Septa Φ20*3mm Temperature Resistant -60℃-200℃ with 9mm 

Wheaton W224224 Aluminum Crimp Seal with PTFE/Butyl Septa for Headspace Vial, 20mm Closure Size (Case of 100): Science Lab Cap Plugs: Amazon.com: Industrial 

20mm Crimp-top Aluminum Caps with Septa ND20 10ml & 20ml crimp top ND20 headspace vial with matched 20mm Aluminum & Magnetic Aluminum cap, 20mm PTFE/rubber 

Vials for gas chromatography (headspace vials) are available in different sizes with standard aluminum seals, magnetic seals or pressure release seals.

20mm Aluminum Seals, Pressure Release, for Headspace & SPME Vials ; 5143PR-20, 20mm Silver Pressure Release Seal, 0.100" PTFE/Silicone Lined, 100 Case, $77.

Cap, crimp, headspace, with septa, 20 mm, silver aluminum cap with safety feature, certified, PTFE/silicone septa, 1000/pk, 10 x 100 pc.

Vials for gas chromatography (headspace vials) are available in different sizes with standard aluminum seals, magnetic seals or pressure release seals.