GPI refers to the "Glass Packaging Institute"

The GPI is responsible for establishing and issuing standards for the types and finishes produced by American glass manufacturers.

For example, and 8-425 neck finish is approximately 8 mm in diameter across the outside of the threads. The 425 represents the finish (style of thread).

               Typical GPI finishes found in the                    chromatography field are as follows:

                   8-425 Closure - Varian, Shimadzu 10-425                    Closure - Waters Alliance 2690 13-425                    Closure - Waters 48 position WISP™,                    Shimadzu.

                   Note: 9 mm thread finish does not appear                    in the GPI finishes. It is not a standard                    finish. The 9 mm closure and vial are used                    with Hewlett-Packard equipment.

Terminology:
Borosilicate - A glass that is high in silicate and having at least 5% boron oxide.

Linear Coefficient of Expansion - Fractional change in length of glass per degree change in temperature. Strain Point - Maximum temperature to which glass should be heated during use.

Types of Glass:
USP Type - Pharmaceutical glass containers can be classified as USP Type I, II, III or NP.

                   Type I - Borosilicate glass represents the                    least reactive glass.
                    Type I glass has the least pH shift. (Lowest                    leaching characteristics)
                   Coefficient of Expansion = 33 or 51 for Clear                    and 51 for Amber

                   Type II - is de-alkalized soda lime glass                    with higher levels of sodium hydroxide                    and calcium oxide.

                   Type III - soda lime glass - cannot be                    autoclaved.

                   Type NP - general purpose soda-lime glass                    used where chemical durability and heat                    shock are not factors.
                   Coefficient of Expansion = 92