NH thread

The short version:

The thread standard for garden hose connectors in the United States, its territories, and Canada is known colloquially as "garden hose thread" (GHT), but its official designation is NH... NH stands for "National Hose"... This fitting is used with ​1⁄2-inch, ​5⁄8-inch, and ​3⁄4-inch hoses.
In other countries, a British Standard Pipe (BSP) thread is used... The GHT and BSP standards are not compatible...
Various adaptors made of metal or plastic are available to interconnect GHT, BSP, NPT, hose barb, and quick connect fittings.

Damn! Even the short version is too long.

Mas largo at Wikipedia, under Garden hose: Standards and connectors:

Garden hoses connect using a male/female thread connection. The technical term for this arrangement is a "hose union". Spigots or sillcocks have male hose connectors only, and the mating end of a hose has a captive nut which fits the threads there.

The thread standard for garden hose connectors in the United States, its territories, and Canada is known colloquially as "garden hose thread" (GHT), but its official designation is NH (NH stands for "National Hose"; ¾-11.5NH is for full form threads as produced by cutting material such as the brass spigot outlet or hose male or female end fitting found on more expensive hoses; ¾-11.5NHR is for thin-walled couplers produced by rolling thin material, usually brass, typically found on less expensive hoses; ¾-14NPSH is for female hose ends that mate a hose to a tapered pipe thread without a spigot). The standard was defined by NFPA 1963, "Standard for Fire Hose Connections",[1] then later by ANSI-ASME B1.20.7,[2] which is 1 1⁄16 inches (27 mm) diameter straight (non-tapered) thread with a pitch of 11.5 threads per inch (TPI). The female thread is abbreviated FHT, and the male part is abbreviated MHT. This fitting is used with ​1⁄2-inch, ​5⁄8-inch, and ​3⁄4-inch hoses.[3][4]

In other countries, a British Standard Pipe (BSP) thread is used, which is ​3⁄4 inch and 14 TPI (male part outside diameter is 26.441 mm or 1.04 in). The GHT and BSP standards are not compatible, and attempting to connect a GHT hose to a BSP fitting, or vice versa, will damage the threads.

Various adaptors made of metal or plastic are available to interconnect GHT, BSP, NPT, hose barb, and quick connect fittings.

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This topic comes up because I was confused. Or maybe I still am. I think "fire hose thread" and "garden hose thread" (GHT) are two kinds of "NH" thread. I think all GHT are NH but not all NH are GHT. Garden hose thread indicates one size of NH specifically. Fire hose thread is bigger and varies in size.

FireHoseDirect has a good info page on fire hose and the NH standard.