NPT - American tapered pipe
3-8 NPT pipe thread: 8 TPI, major Ø 88.9 mm.
Profile
| Designation | 3-8 NPT |
|---|---|
| Major (outside) diameter | 88.9 mm · 3.5" |
| Pitch | 3.175 mm · 8 TPI |
| Pitch diameter | 86.838 mm · 3.4188" |
| Minor diameter (external) | 85.005 mm · 3.3466" |
| Minor diameter (internal) | 85.463 mm · 3.3647" |
| Recommended tap drill | 82.7 mm |
Pipe threads are made up to a seal against the mating flanks, not tightened to a bolt preload, so no proof load or tightening-torque figure applies.
The bolt schedule collects the fasteners for one job onto a single sheet - tap drill, wrench size, grade and tightening torque on every line, taken straight from pages like this one. Free schedules hold 3 lines and are saved in this browser only.
3-8 NPT is a NPT pipe thread running at 8 threads per inch on a 88.9 mm major diameter. NPT is a 60° tapered thread that seals on the flanks; use a tapered reamer after drilling for a full-form thread.
All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables - not hand-entered. See the full reference.
Drill 82.7 mm before tapping 3-8 NPT. NPT is a 60° tapered thread that seals on the flanks; use a tapered reamer after drilling for a full-form thread.
3-8 NPT is tapered. NPT is a 60° tapered thread that seals as the flanks wedge together, normally with thread sealant or PTFE tape.
3-8 NPT runs at 8 threads per inch, a pitch of 3.175 mm, on a major diameter of 88.9 mm.
No. Pipe threads are made up to a seal against the mating flanks, not tightened to a bolt preload, so no proof load or tightening-torque figure applies.
The pipe this thread runs on
NPS 3 pipe is 3.5 in across the outside whatever the schedule; at standard wall (std) the wall is 0.216 in and the bore 3.068 in.
Full dimensions for the standard wall · every schedule in the chart
Nearby sizes