ThreadRef

Sizes · Pipe (NPT / BSPT / BSPP)

NPT — American tapered pipe

3-8 NPT

3-8 NPT pipe thread: 8 TPI, major Ø 88.9 mm.

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Tap drill
82.7 mm
88.9 mm major Ø

Profile

Thread form & key diameters

Major Ø 88.9 mmP 3.175 mm60°Root Ø 85.005 mm · Pitch Ø 86.838 mm3-8 NPT8 TPI · 60° form

Dimensions

Designation3-8 NPT
Major (outside) diameter88.9 mm · 3.5"
Pitch3.175 mm · 8 TPI
Pitch diameter86.838 mm · 3.4188"
Minor diameter (external)85.005 mm · 3.3466"
Minor diameter (internal)85.463 mm · 3.3647"
Recommended tap drill82.7 mm

What tap drill do I need for 3-8 NPT?

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.

Nearby sizes

More npt — american tapered pipe threads

2-1/2-8 NPTTap 67.06 mmØ 73.03 mm · pitch 3.175 mm2-11.5 NPTTap 56.36 mmØ 60.33 mm · pitch 2.209 mm1-1/2-11.5 NPTTap 44.05 mmØ 48.26 mm · pitch 2.209 mm1-1/4-11.5 NPTTap 38.1 mmØ 42.16 mm · pitch 2.209 mm1-11.5 NPTTap 29.36 mmØ 33.4 mm · pitch 2.209 mm3/4-14 NPTTap 23.42 mmØ 26.67 mm · pitch 1.814 mm1/2-14 NPTTap 17.86 mmØ 21.34 mm · pitch 1.814 mm3/8-18 NPTTap 14.68 mmØ 17.15 mm · pitch 1.411 mm