1/4 NPT Thread Specs
Standard: ASME B1.20.1 (NPT)
Technical parameters and design data for the 1/4 NPT pipe thread.
Established under standard ASME B1.20.1, this thread uses a pitch of 0.05556 inches and has 18 threads per inch.
Often used in fluid, hydraulic, or pneumatic systems, NPT/BSP threads require suitable thread sealants to assure leak-tight performance.
Dimensional Specifications
Size Designation
1/4 NPT
Nominal Diameter
0.54 in(13.72 mm)
Major Diameter
0.6798 in(17.27 mm)
TPI (Threads per Inch)
18
Pitch
0.05556 in
Pitch Diameter
0.6437 in(16.35 mm)
Minor Diameter
0.6197 in(15.74 mm)
Tap Drill size
7/16 in
Quick Unit Converter
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Frequently Asked Questions
What is the tap drill size for 1/4 NPT pipe thread?
The recommended tap drill size for a 1/4 NPT pipe thread is 7/16 inches.
What is the major diameter of a 1/4 NPT pipe thread?
For a standard 1/4 NPT pipe thread, the major diameter at the pipe reference plane is 0.6798 inches (approx. 17.27 mm).