This specification provides standard dimensional requirements for glass filtering flasks suitable for general laboratory use. Glass filter flasks shall be in the following types: Type I, Type II (Class 1 and Class 2), and Type III (Class 1, Class 2, and Class 3). Flasks shall be made of the specified borosilicate glass and shall conform to the prescribed maximum residual thermal stress. The general appearance of the flasks are illustrated. The design for (1) conical flasks including bottom concavity and bottom heel radius, (2) neck finish, and (3) side-arm are specified. Filtering flasks shall conform to the prescribed requirements for (1) capacity; (2) dimensions such as body outside diameter, overall height, rubber stopper size, bottom and heel wall thickness, and base/heel radius; and (4) pressure resistance. Each flask shall be permanently marked with the name or known trademark of the manufacturer and the nominal capacity. There shall be an area on one side of the flask for marking with a pencil.