When to use PTFE teflon yellow or white tapes or pipe dope
The purpose thread seal tape (also known as “Teflon tape”) or pipe dope, there are three:
First, the quality of lubricating oil so that the male is opened deeper inner threaded fittings to prevent leakage;
Second, it acts as a filler to smooth the thread micro scratches or surface irregularities;
Third, it is the male and female threads together Rusty (aka catch);
There are many comments about the early photographs show the sealing tape that is wrapped in the wrong direction (thank you for pointing out my supervision).