20mm Crimp Neck Closures Factory--Aijiren Vials for HPLC/GC. This is because Crimp Top Headspace Vial is widely used in gas chromatography. The 20mm Crimp Neck Closures are made of high-quality aluminum. The central hole with a large opening is convenient for autosampler injection. , Septa is compounded with Silicone and PTFE as raw materials.