An international acceptable series of flasks is specified concluding: round-bottom, flat-bottom and conical flasks. Two series are specified for each type of round-bottom and flat-bottom flasks. The series differ in heigt and in selection of joint sizes. For conical flasks one series of heights is specified each having different joint sizes. The material must be borosilicate glass 3.3. For the three types of flasks the capacities and the series with overall height and joint size are tabled.