Like water pipes, supply lines in the U.S. UU. They are threaded with a conical thread on the right. Reverse threads are used to prevent accidental connection to something other than the intended purpose of the gas coupling.
Some plumbing fixtures have reverse threads to prevent incorrect lines from being mistakenly connected to the electrical outlet. Gases such as oxygen and acetylene have reverse threads so that the hoses cannot mix and cause a fire or explosion. They have standard right hand threads on one side %26 reverse (left) threads on the other. They are usually used for gas pipes, when joints are not allowed.
Typically, reverse thread nozzles only come in 4 lengths. But they do make dies for cutting inverted threads, and most plumbing supply houses should have them to cut you a little, but it's probably a little more expensive than you'd expect. Water heaters also need some type of dielectric connection from the steel tank if copper tubing is used. Fun fact, brazed copper is a type of pipe and fitting acceptable for residential natural gas in much of the U.
If you tighten the fittings too tight, you can strip the threads inside the fitting or on the outside of the pipe. Turning a screw, opening a jar or bottle, operating a faucet, and adjusting a plumbing fixture all work on the same principle. Garden hoses are also made not to interconnect with normal pipes so that idiots don't connect your house with garden hoses.