Iron pipe size, or IPS, refers to an older system that categorizes the thickness of pipe walls, still used by some manufacturers of iron and polyvinyl chloride, or PVC, piping that connects to faucets for home and business use.
Types of piping categorized by the IPS system for faucets include a female IPS, often called female iron piping, or FIP, which has internal threads for joining piping together. The installer inserts a section of FIP into another section, then twists it to tighten. The other type -- male iron piping or MIP -- contains threading on the outside of the pipe.
During the height of IPS system use, before the second world war, metal piping relied on halves welded together. Users of the piping found diameters by measuring the outside diameters, or ODs, which closely resemble the pipe sizing system widely used today: the ductile iron pipe standard, or DIPS.
Philadelphia replaced its wooden water piping system in 1804 with cast-iron pipe, marking the first time a city switched to all-iron piping, reports ThePlumber.com. Able to supply city residents with plentiful water from the Schuykill River, Philadelphia then sold its old wooden piping to the city of Burlington, New Jersey.