Crimp Top Vials,Headspace Vials,20ml Vials,GC Vials 18mm Screw Neck Headspace Vial for GC--Aijiren HPLC Vials 18mm Screw Thread top septa is used PTFE and high-quality silicone rubber or ultra-pure silica as raw materials, the gasket is guaranteed to be non-toxic.