Introduction
In plumbing, two types of threads are used - National Pipe Thread (NPT) and Female Iron Pipe (FIP). These threads are important to know in order to properly connect two pipes or fittings.
NPT Threads
National Pipe Thread (NPT) is a standard type of thread used in plumbing. It is a tapered thread, meaning that the diameter of the thread decreases as it gets closer to the end of the fitting. This design allows for a tighter seal, as the tapering creates pressure that seals the connection.
NPT threads are used on male fittings, such as pipes or nipples. The internal threads of a female fitting, such as a coupling or elbow, match the external threads of the male fitting. The threads are typically coated with a thread sealant, such as teflon tape or pipe dope, to ensure a secure connection that is leak-free.
FIP Threads
Female Iron Pipe (FIP) threads, also known as Female National Pipe Threads (FNPT), are another type of thread used in plumbing. FIP threads are straight threads, meaning that the diameter of the thread remains the same throughout the fitting. Unlike NPT threads, FIP threads do not taper, which can make them easier to connect and disconnect.
FIP threads are found on female fittings, such as couplings or elbows, and are typically used to connect to pipes or nipples with male NPT threads. As with NPT threads, FIP threads are typically coated with a thread sealant to ensure a secure and leak-free connection.
Differences
The main difference between NPT and FIP threads is their design. NPT threads are tapered and are used on male fittings, while FIP threads are straight and are used on female fittings.
Another difference is their compatibility. NPT threads are compatible with other NPT threads, while FIP threads are compatible with other FIP threads. In order to connect an NPT male fitting to an FIP female fitting, an adapter with both NPT and FIP threads would be required.
When to Use NPT or FIP Threads
The choice between NPT or FIP threads depends on the specific plumbing application. NPT threads are typically used in gas or liquid applications that require a tight seal, such as in piping systems or machinery. FIP threads are often used in water applications, such as connecting a showerhead or faucet.
It is important to note that NPT threads are not recommended for plastic fittings, as the threads can easily damage the material. In these cases, FIP threads are a better option as they are less likely to cause damage.
Conclusion
In summary, NPT and FIP threads are two types of threads used in plumbing. NPT threads are tapered and used on male fittings, while FIP threads are straight and used on female fittings. The choice between NPT or FIP threads depends on the specific plumbing application and compatibility, and it is important to use the appropriate thread type to avoid damage and ensure a secure connection.