Known by a number of other names including thread seal tape and plumber's tape, Teflon tape is primarily used to seal the threads around pipe. The way it works it simple: before a threaded pipe is joined with a female-threaded link piece, the pipe threads are wrapped with Teflon tape. As the pipe is screwed into place, the malleable Teflon is compressed and fills the gaps in the thread. The immediate result of this is that the seal between the pipe and linkage piece is made entirely air and waterproof.
Threads that Work with Teflon Tape
There are two basic types of threads: tapered threads and parallel threads. Teflon tape is only useful with tapered threaded material, for this type forms a seal due to the wedging action of a male-ended thread into the female end. Parallel threads, such as found on a nut/bolt combination, will not bond with Teflon tape because the nature of the threads do not inherently form a seal.
Teflon Tape Uses
For pipe work involving pressurized water, Teflon tape is regularly used to create the seal necessary to help prevent leaks. Other uses for Teflon tape include work on centralized heating systems and air compression devices. In both of these latter cases, the Teflon tape serves to create the same type of airtight seal it does in plumbing applications.