A lot of people keep asking what to use for flashes, Zoom recorders, professional shock mount 
microphones adapters and their DSLR

1/4″ 20 threads per inch is the thread size used on photo and video camera mounts and tripods. Your DSLR camera is having a 1/4″ thread female mount and your DSLR tripod is a 1/4″ thread male mount. Professional microphones (like those you see on stage at rock concerts 🙂 ) use 3/8″ and 5/8″ thread mounts.

The 5/8″ 27 threads per inch  mount is popular in USA, while the 3/8″ 16 threads per inch (55° flank angle) are more popular in Europe.

For example, a usual zeppelin (blimp) shockmount would usually have a 3/8″ female mount. An usual stage microphone clip would have a 5/8″ female mount but they most of the time come with a simple to 3/8″ adapter or a double 3/8″ and 1/4″ adapter.

Zoom recorders (like the popular Zoom H1) are different beasts. Since they are built for photo and video enthusiasts, they come with a 1/4″ thread. This way, they can be mounted directly on your photo tripod, without any adapter.

I hope this crazy thread thing is more clear now for you.
Oh, and I did NOT opened the 55° vs. 60° flank angle subject 😀