Understanding the Differences Between Common Threads: NPT, MNPT and FTP

For those working with thread arrangements for piping, it’s important to know the differences between types of threads. Whether NPT vs. MNPT, FTP vs. NPT, or even NPT vs. BPT, understanding the differences between these commonly used threads will help avoid issues from utilizing incompatible pipe threads.

Understanding & Determining Common Thread Types

Identifying common piping thread types requires a caliper, thread gauge, and reference chart. The gauge helps determine the thread’s pitch, diameter, and angle. Featuring jagged teeth like a saw, it ensures a thread falls between an upper and lower limit, with a specific number of serrations marking the parameters that are also normally marked. For US standard threads, the pitch is determined by the number of threads per inch, while metric-based standards measure the distance in millimeters between each thread.

Steps to help determine the type of thread: 

  • Identify whether the thread is parallel or tapered. This may be possible by visually inspecting the threads, with parallel threads having the same diameter throughout and tapered threads growing smaller toward the fitting’s end. A caliper can compare thread diameters if a visual inspection doesn’t reveal this.
  • Establish the thread’s pitch. A pitch gauge is used to either compare threads against a lighted background when utilizing the American standard or to measure and calculate the number of threads within a given distance when using a metric standard. Results from this step determine the different thread forms by narrowing down the possibilities.
  • Verify the size of the thread. For pipe threads, determining size is done by comparing the thread’s size profile; for pipes below 2 inches, the nominal size can be verified by measuring the outside diameter, subtracting ¼ inch, and rounding the measurement.
  • Describe the thread. This step involves designating the industry standard under which the thread will be described to allow maintenance or installation personnel to understand the type and size of the thread with which they’re working, along with the pitch in certain instances. This is where the reference chart comes in, which enables workers to

Following the above four steps helps minimize downtime and expenses from ordering the wrong components.

Comparisons of Common Threads

When comparing NPT vs. BPT, FTP vs. NPT, or NPT vs. MNPT, it’s important to establish whether the thread is parallel or tapered. To do this involves measuring the first and last full threads, along with the fourth or fifth one. It’s tapered when the diameter increases between the first and last threads on a male thread or decreases for a female thread. However, it’s considered a parallel thread if the thread diameter stays the same.

Once determined to be tapered or parallel, its trade size can then be measured. Tapered threads are measured at the fourth or fifth full thread to ascertain trade size, whereas parallel threads can be measured at any full thread. Once properly measured, the measurement can be referenced via a table to match the thread and trade size.

Some common types of pipe threads used in stainless steel applications include:

  • National Pipe Tapered Thread (NPT) is a US thread standard with a 60-degree thread form on a tapered thread, with a taper of ¾ inch per foot.
  • Male national pipe thread (MNPT) is the male version of NPT pipe thread, sometimes abbreviated as MPT or NPT(M).
  • Female pipe thread (FPT) is the female version of NPT pipe thread, sometimes abbreviated as NPT(F).
  • British pipe thread (BPT) is utilized by the United Kingdom and many member countries of the British Commonwealth that feature an un-tapered thread form of 55 degrees.


NPT is the most used thread for pipes and fittings for connecting hydraulic seals and mechanical joints. Two different kinds are used for sealing hydraulic circuits. Jointing threads tighten pressure by sealing on the threads, with a jointing compound improving this sealing effect; these feature taper external threads, along with either parallel or taper internal threads. In contrast, fastening threads don’t seal on the threads, using two threads in parallel to provide pressure upon a flat gasket or soft material against the external thread.

The general features of NPT are:

  • Measurement of pitch is the number of threads per inch.
  • Taper to the center axis is at an angle of 1.7899° for the pipe or fitting.
  • Root shortness and peaks are more level.
  • Thread angle of 60°.

MNPT is simply the male version of the NPT standard, with male or external tapered threads. When considering whether to utilize NPT vs. MTNP, it should be noted that the latter is interchangeable with the NPT standard.


When considering the differences between FPT and NPT standards, it should be noted that the FPT standard features internal tapered pipe threads. Essentially the female NPT standard can connect with their male NPT counterparts, joining pipe sections and fittings. They’re used in dry-seal connections, especially those involving fuel applications. FTP connections don’t require tape or other sealants like regular male NPT threads. Unlike NPT vs. MNPT, they aren’t interchangeable but rather interlocking.

These threads feature the same basic shape as the NPT standard but eliminate spiral leaking by adjusting root and crest heights, creating an interference fit. FPT vs. NPT largely differs between the former having internal threads, whereas the latter male standard is external. When making tapered connections with FPT, NPT fittings lock into their female counterparts, expanding until the force between them can withstand the pressure of whatever material flows through the pipes. Though FPT threads require no sealant on their own when connecting with male NPT threads sealant is required because of the narrow clearance between the male piece’s root and crest.


However, when comparing BPT vs. NPT threads, the differences are much more marked. Whereas American standard measurements count the number of threads per inch with NPT, BPT utilizes the metric system to measure the distance between threads. BPT also has a thread flank angle of 55° for parallel and tapered threads, whereas NPT’s thread form is 60°. They do have a couple of similarities, however. When considering BPT vs. NPT fittings, both can be used with pipes of standard size. Additionally, both are difficult to seal, requiring sufficient compression on the pipe’s threads to form a seal.

For more information about how our company can help with your application – or to learn more about comparisons of common pipe threads like NPT vs. MNPT, FTP vs. NPT, and BPT vs. NPT – we invite you to contact the experts at Arthur Harris today.