3/8-18 NPT thread: 17.15 mm × 18 TPI
Threads › 3/8-18 NPT
3/8-18 NPT is an NPT taper thread: 17.15 mm pipe OD, 18 TPI (1.411 mm pitch), 60° form. Tap drill 14.7 mm. Taper thread: the Ø changes along the length, measure near the start.
| Standard | NPT taper |
|---|---|
| Pipe OD | 17.145 mm (0.675″) |
| Pitch | 18 TPI (1.411 mm) |
| Thread angle | 60° |
| Tap drill | 14.7 mm |
Open 3/8-18 NPT in BenchsmithAdd to order list
Measure it
Bolt: Measure across the crests of the bolt with the caliper jaws. Worn bolts read 0.1 to 0.3 under.
Nut or tapped hole: Measure across the tops of the threads inside the nut or hole with the inside jaws. That is the minor Ø. Worn or oversize holes read a little over.
Close in size, won't mate
- G3/8Ø16.66 mm, 19 TPI
- R3/8Ø16.66 mm, 19 TPI
- M18Ø18 mm, 2.5 mm pitch
- M18×1.5Ø18 mm, 1.5 mm pitch
- M18×2Ø18 mm, 2 mm pitch
- Tr18×4Ø18 mm, 4 mm pitch
One size up or down
- 1/4-18 NPTØ13.72 mm (down)
- 1/2-14 NPTØ21.34 mm (up)
Got a bolt and no idea what it is? Measure the outside Ø and type it into Benchsmith → Find → Thread.