NPT thread (conical pipe thread) is the American standard 60-degree tapered pipe thread, and its size specification is very detailed, covering a number of parameters, the following is a detailed introduction to the NPT thread size:
NPT Thread Size Designation
Usually in inches, such as 1/8, 1/4, 3/8, 1/2, 3/4, 1, etc., these sizes indicate the diameter of the thread.
Threads per inch (TPI): indicates the number of thread teeth per inch of length, and this value determines the pitch of the thread. For example, NPT 1/4 threads have a TPI of 18, which means there are 18 threaded teeth per inch.
Large Diameter, Medium Diameter, Small Diameter:
Large diameter: the largest diameter of the thread, also known as the outside diameter.
Medium Diameter: The average diameter of the thread, located between the large and small diameters.
Small diameter: the minimum diameter of the thread, also known as the inner diameter.
Examples of specific sizes of NPT threads
NPT1/4 threads:
Threads per inch (TPI): 18
Outside diameter: 0.540 inches (13.616mm, this is converted to millimeters after the large diameter size)
Large diameter: 13.616mm
Medium Diameter: 12.487mm
Small Diameter: 11.358mm
Pitch: 25.4mm / 18 = 1.411mm
Thread height: 1.129mm
Thread length: Effective length 9.5mm, from pipe end to base 5.080mm
Pipe end thread ID: 10.997mm
NPT1/2 thread:
Large diameter: 21.223mm
Medium diameter: 19.772mm
Small diameter: 18.321mm
Other features of NPT thread
Taper: The taper of NPT thread is 1:16, i.e. the angle between the mother line of the cone and the axis is 1 degree 47 minutes 24 seconds (about 1.7899°).
Sealing performance: Due to its larger taper and thinner tooth shape, NPT thread has good sealing performance and is commonly used in pipe connections that require sealing.
Fitting mode: The fitting mode of NPT thread consists of “cone/taper” fitting and “column/taper” fitting, i.e. the fitting of conical inner thread and conical outer thread, or the fitting of cylindrical inner thread and conical outer thread.
NPT Thread Size Specifications
NPT thread size specification consists of several parameters such as thread size designation, number of threads per inch, large diameter, medium diameter, small diameter, etc. These parameters together determine the size of NPT threads. These parameters together determine the geometry and size of NPT threads, and also affect their sealing performance and fit. In practical applications, the appropriate NPT thread size specification should be selected according to specific needs.
