What type of threads should be used to create a proper seal when installing pipe?

The proper seal when installing pipe is achieved using tapered pipe threads. Tapered threads are designed so that the diameter of the thread gradually decreases as it goes down the length of the pipe. This taper creates a tight fit as the male and female parts are screwed together, allowing for compression that seals the joint effectively. This is crucial in plumbing where leaks can cause significant issues.

Tapered threads provide a mechanical seal along with the potential for additional sealing materials, such as Teflon tape or thread sealant, to enhance the effectiveness of the joint. The design of tapered threads allows them to create an excellent seal under pressure, making them suitable for various applications, including water and gas.

Other types of threads, while they may have their specific uses, do not provide the same sealing capability when it comes to piping applications. For example, UN threads are not designed for sealing and are more common in machinery and automotive applications. Metric threads are standardized for different applications but generally do not create a seal on their own. Square threads are typically used in mechanisms where load engagement and backlash are considerations, but are not suitable for creating a fluid or gas tight seal in pipe connections.