Teflon tape is a thread sealing tape meant for threaded pipe. To use Teflon tape, you must wrap 3 to 5 layers on the male pipe threads. Make sure you wrap clockwise! Attach your pipe fitting and tighten. There are four main types of Teflon tape: White (low destiny). This Teflon tape is the cheapest, and can be found at any hardware store. It does not seal too well and is only good for up to about 120 PSI. Yellow (medium density) tape is often used for gas. It can be found at any hardware store, and is good for high pressures or large pipe. This tape costs a little more than the white kind. Pink (medium density) is like the yellow Teflon tape, but it is not rated for gas. It can be found at some hardware stores or online. Grey (medium density) is for stainless steel. This tape is found online. There is a little nickel in this tape that prevents galling. Green (medium destiny) Teflon tape is made for oxygen. DO NOT use other types of tape for oxygen, as there is an explosion hazard.
Teflon tape comes in several widths. The most common one is 1/2 inch, but widths up to 2 inches are available at industrial supply stores or online. There is also pipe dope, which is a liquid that is used like Teflon tape. For spud guns, it is best to use one rated for high vibration. I like to use Rectorseal Tru-Blu, which can be found at a hardware store or online. Pipe dope is required for large threads or extremely high pressure. It cannot be used for oxygen service. Pipe dope comes in a can with a brush in the lid. It is brushed onto the pipe threads. The parts are threaded together, and excess dope may be cleaned off, if desired. Pipe dope also comes in a tube that is squeezed onto the threads. For exceptionally high pressures or high pressure with large threads, pink or yellow Teflon tape may be used, then a layer of dope applied over it.