GC Vials ND20 headspace 20ml (Crimp Vials) 20mm Aluminum Crimp Cap Seals and Vials ensure that a proper seal is made for this demanding application . Vials are manufactured of Clear, Type 1 Class A or Amber, Type 1 Class B borosilicate glass and include a write-in patch for sample identification. Both flat and rounded bottom vials are available.