In addition to the vials volume (1ml, 2ml, 4ml, ), they are differences in vials type (screw, crimp, crimp or snap, shell), material (clear glass, amber glass, polypropylene), dimensions (12x32mm, 15x45mm, ), diameter (8mm, 9mm, 10mm, 11mm, ), just select all these parameters to determine the part number for your specific needs.