Diameter: 17mm, 19mm, 24mm 

Best condition for measurment： Water bath Oil-bathing 
Distillation flask a kind of glass container that is used for liquid distillation or fractionation material often and condense a pipe to connect liquid pipe to connect liquid implement form a complete set to use, make it commonly so 3 neck, also can assemble gas generator，corrosion resistant resistance to hydrofluoric acid