All screw threads vials and caps are differentiated by their thread finish as defined by the Glass Packaging Institute, GPI. For screw thread vials, a two part number is assigned. For example, 8-425 neck finish represents a vial with a diameter of 8 mm across the outside of the threads and a thread style of
425. Screw thread vials and caps are more expensive than crimp seals.
Crimp top vials
Require lacquered aluminum crimp seals which are relatively inexpensive and, when properly assembled, provide the best seal for long term storage. Crimp seals are not reusable. A crimping tool is required to seal caps and a decrimper or decapper is required to remove the seals.
Snap seal vials
The snap vials are compatible with either crimp and/or snap seals and no special tools are required to remove the cap. These vials are recommended for short term sample storage and non-volatile samples because the seal is not as secure as a crimp or screw thread seal.