3-1/2 NPT Thread Specs
Standard: ASME B1.20.1 (NPT)
Technical parameters and design data for the 3-1/2 NPT pipe thread.
Established under standard ASME B1.20.1, this thread uses a pitch of 0.125 inches and has 8 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
3-1/2 NPT
Nominal Diameter
4 in(101.6 mm)
Major Diameter
4.4313 in(112.56 mm)
TPI (Threads per Inch)
8
Pitch
0.125 in
Pitch Diameter
4.3501 in(110.49 mm)
Minor Diameter
4.296 in(109.12 mm)
Tap Drill size
3-3/4 in
Quick Unit Converter
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Frequently Asked Questions
What is the tap drill size for 3-1/2 NPT pipe thread?
The recommended tap drill size for a 3-1/2 NPT pipe thread is 3-3/4 inches.
What is the major diameter of a 3-1/2 NPT pipe thread?
For a standard 3-1/2 NPT pipe thread, the major diameter at the pipe reference plane is 4.4313 inches (approx. 112.56 mm).