ISO 9187 categorizes ampoule into the following three: Form B, Form C, and Form D.
The factor to classify the type of ampoule is up to the shape of funnel. The funnel of Form B is made by cutting its "stem" part first using a motor and then glazing it with fire. Its funnel is weak and costs a large amount of raw materials.
Form C is the most widely used ampoule. Its "stem" part is processed with flame, which makes the funnel strong and causes less foreign substances.
Form D has a closed funnel, which makes it possible to inject the fluid at the opening. Cleansing process is unnecessary.
The above three ampoules are a vertical type of Europe. "Flame Cut" ampoule is the horizontal type of Japan, which straightly processes "stem" part and makes only the funnel part open.