2. Screw Thread (Long Term) 3. Polyethylene Snap Caps (72 hour storage) 4. Polyethylene Snap Plugs (Single Use) 2,Why choose crimp cap vials? Crimp caps provide the tigh test seal,reducing the chance of sample evaporation.the 11.6*32mm crimp vials and 11mm aluminium crimp caps are economical and easy touse with vials crimping tools.