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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.

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 compatability 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
         
Austin, TX NS 4 6
Charlotte, NC NS 4 6
Chicago, IL     4.5 6
Cleveland, OH 2.5 8 4.25 6
Colorado Springs, CO NS 4.5 6
Columbus, OH - - 4 6
Dallas. TX NS 4 4
Denver, CO NS 4.5 6
El Paso, TX NS 4 6
Fort Worth, TX NS 4 4
Indianapolis, IN NS    
Kansas City, MO NS 4 4
Las Vegas, NV NS 4 4
Los Angeles, CA NS 4 4
Memphis, TN NS 4 7
Miami, FL NS 4 7
New Orleans, LA 2.5 6 NS
New york City, NY 2.375 8 NS
Oklahoma City, OK 2.5 6 NS
Phoenix, AZ 2.5 6 4 6
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
Seattle,WA NS 4 6
Tulsa, OK NS 4 4
Washington, DC NS 4 4
Wichita, KS NS 4 4

Thread Type Compatibility

In order for two components to fit properly, thread types must be compatible. See the list below for thread types that can be used together.

 ** We had previously indicated GHT as compatible with 3/4-NH.  This was incorrect.  Oops... sorry.

Federal Specification WW-C-621G

WW-C-621G
February 7, 1990
SUPERSEDING
WW-C-621F
April 4, 1983

FEDERAL SPECIFICATION

COUPLING ASSEMBLY, HOSE (FIRE, WOVEN-JACKETED,

RUBBER- OR FABRIC-LINED AND UNLINED)

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
 1/16"
27
---
 1/8"
27
28
 1/4"
18
19
 3/8"
18
19
 1/2"
14
14
 5/8"
---
14

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
 3/4"
14
14
1"
11 1/2
11
1 1/4"
11 1/2
11
1 1/2"
11 1/2
11
2"
11 1/2
11
2 1/2"
8
11

 
Pipe Size
Pitch  (Threads/Inch)
NPT/NPS
BSP
3"
8
11
3 1/2"
8
11
4"
8
11
5"
8
11
6"
8
11
8"
8
---