Z stand for borosilicate glass type: 7 : 7.0 type; 3 & 5 means 5.0 type VA, VH, VHR are stand for headspace vials, VA is screw headspace vial, VH is crimp headspace vial, R is stand for Round Bottom. For Example: V2015,20 means 20ml, 1 means clear color, 5 means 5.0 type, so V2015 means 20ml clear EPA vial , 5.0 type.