Thread Identification
The following information is intended to aid in identifying threads for (NH) American National Fire Hose Thread, sometimes designated as (NST) National Standard Thread, or (NS) National Standard. Threads not conforming to these specifications should be considered as "Specials".
Additional details on thread specifications may be found in the National Fire Protection Association's Standard NFPA 194-1974. This standard applies for thread connections on fire hose couplings, suction hose couplings, relay supply hose couplings, fire pump suctions, discharge valves, fire hydrants, nozzles, caps, adapters, reducers, plugs, wyes, siamese connections, standpipe connections, and sprinkler connections.
| Nom. Size | Threads Per In. | Flow Dia. | External Threads Major O.D. | Internal Threads Manor L.D. |
|---|---|---|---|---|
| ¾ | 8 | ¾" | 1.3750" | 1.2246" |
| 1 | 8 | 1" | 1.3750" | 1.2246" |
| 1½ | 9 | 1½" | 1.9900" | 1.8577" |
| 2½ | 7.5 | 2½" | 3.0686" | 2.9104" |
| 3 | 6 | 3" | 3.6239" | 3.4223" |
| 3½ | 6 | 3½" | 4.2439" | 4.0473" |
| 4 | 4 | 4" | 5.0109" | 4.7111" |
| 4½ | 4 | 4½" | 5.7609" | 5.4611" |
| 5 | 4 | 5" | 6.2600" | 5.9602" |
| 6 | 4 | 6" | 7.0250" | 6.7252" |
