Why are there different threads?
There are 3 main types of threads for fire hose: NY Corp, FDNY and National Standard. Alot of it goes back to the 1800's and early 1900's when there was no standardization. Nowadays its usually addressed in the building code.
NYC requires FDNY threads on hydrants and standpipes. Yonkers requires NY Corp threads. I've heard stories where companies on routine drills found standpipes where there were different threads on different floors based on who did the install.
Most of the older cities along the east coast figured it out after they burned half of their cities down. There's a story that during the Great Baltimore Fire, FDNY sent pumpers down on trains and they couldn't pump any water due to not having the right threads to hook into Baltimore's hydrants.
After 9/11 there was a big push by the FDNY to make sure the surrounding department's had adaptors for operating in NYC. This was addressed through annual interoperability training days. In Westchester, you can find all three types throughout the county, and even a few 1-off thread types. Most of the career departments carry a full set of adaptors on every rig. From what I understand, the border companies in the city do too. That also includes the magnetic hydrant wrenches used in NYC and Yonkers and wrenches for the new style "minion" hydrants popping up in the Sound Shore area.