Everything has a standrad, not only for the nature, but also applied in the metal world. Like the Self Tapping Screws, you can list a lot kinds of it, but you maybe do not know the engineering standrads of Sel Tapping Screws.
The size of Self Tapping Screws, machinery, functional performance has the following engineering standards:
ANSI/ASME B18.6.4-Thread Forming And Thread Cutting Self Tapping Screws And Metallic Drive Screws (Inch Series)
SAE J933-Mechanical and Quality Requirements For Self Tapping Screws