1/4-18 NPT thread: 13.72 mm × 18 TPI
Threads › 1/4-18 NPT
1/4-18 NPT is an NPT taper thread: 13.72 mm pipe OD, 18 TPI (1.411 mm pitch), 60° form. Tap drill 11.1 mm. Taper thread: the Ø changes along the length, measure near the start.
| Standard | NPT taper |
|---|---|
| Pipe OD | 13.716 mm (0.54″) |
| Pitch | 18 TPI (1.411 mm) |
| Thread angle | 60° |
| Tap drill | 11.1 mm |
Open 1/4-18 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
- M14Ø14 mm, 2 mm pitch
- M14×1.5Ø14 mm, 1.5 mm pitch
- Tr14×3Ø14 mm, 3 mm pitch
- G1/4Ø13.16 mm, 19 TPI
- R1/4Ø13.16 mm, 19 TPI
- 9/16-12 UNCØ14.29 mm, 12 TPI
One size up or down
- 1/8-27 NPTØ10.29 mm (down)
- 3/8-18 NPTØ17.15 mm (up)
Got a bolt and no idea what it is? Measure the outside Ø and type it into Benchsmith → Find → Thread.