Fire Hydrant Standards
There are several different fire hose coupling standards in use in the U.S. today. The trend toward national standardization has been very slow and long in coming. The first real effort in national standardization commenced in the wake of the Great Baltimore Fire of 1904 over one hundred years ago, and it is still far from complete. Many cities and municipalities continue to use their own standard couplings, and some may have different standards from one neighborhood to another. Most couplings in use today are NST standard, with several notable variants, New york City, and Chicago, in particular. See this interesting article for details: NISTIR 7158.
Here is a partial list of some cities and the dimensions of their Fire Hydrant Fittings. The National Standard (NS) Hydrant has two carry hose male fittings of 2.5 inch NST/NH and one pumper fitting of 4.5 inch NST/NH.
It should be noted that some of the hydrant fittings below, that are not NS compliant, might very well be an NST/NH fitting of a different nominal diameter, although some clearly are not, since their diameter and pitch do not match an NST/NH spec. Furthermore, since these diameters are nominal values relating to a given hose size, and not the actual thread diameter, they cannot be used to assure NST/NH compatibility without more precise dimensional information, e.g. pitch diameter.
Fire Hydrant Connections
|Carry Hose||Pumper Hose|
|City||Nom. Dia||Thds/Inch||Nom. Dia||Thds/Inch|
|NS - National Standard (follows NST -also NH)||2.5||7.5||4.5||4|
|Colorado Springs, CO||NS||4.5||6|
|El Paso, TX||NS||4||6|
|Fort Worth, TX||NS||4||4|
|Kansas City, MO||NS||4||4|
|Las Vegas, NV||NS||4||4|
|Los Angeles, CA||NS||4||4|
|New Orleans, LA||2.5||6||NS|
|New york City, NY||2.375||8||NS|
|Oklahoma City, OK||2.5||6||NS|
|San Antonio, TX||NS||4||4|
|San Diego, CA||NS||4||4|
|San Fransisco, CA||3, 3.5||3||3, 3.5||3|
|San Jose, CA||NS||4||4|
|Santa Ana, CA||NS||4||4|