Iron pipe size
Iron Pipe Size (IPS) refers to an old pipe sizing system still in use by some industries, including major PVC pipe manufacturers, as well as some legacy drawings and equipment.
The iron pipe size standard came into being early in the 19th century and remained in effect until after World War II. The IPS system was primarily used in the US and the United Kingdom. In the 1920s, the Copper Tube Size (CTS) standard was combined with the IPS standard.