1/8 BSW thread: 3.18 mm × 40 TPI
Threads › 1/8 BSW
1/8 BSW is a BSW Whitworth thread: 3.18 mm major diameter, 40 TPI (0.635 mm pitch), 55° form.
| Standard | BSW Whitworth |
|---|---|
| Major diameter | 3.175 mm (0.125″) |
| Pitch | 40 TPI (0.635 mm) |
| Thread angle | 55° |
| Minor diameter, bolt | 2.36 mm |
| Minor diameter, nut | 2.36 mm |
| Tap drill | Not listed. Check your tap maker's chart. |
Minor diameters worked out from the basic profile: major Ø − 1.28065 × pitch.
Open 1/8 BSW 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.
Same diameter, other pitch
- #5-40 UNC40 TPI (0.635 mm pitch)
Close in size, won't mate
- M3Ø3 mm, 0.5 mm pitch
- #4-40 UNCØ2.84 mm, 40 TPI
- #4-48 UNFØ2.84 mm, 48 TPI
- #6-32 UNCØ3.51 mm, 32 TPI
- #6-40 UNFØ3.51 mm, 40 TPI
- M2.5Ø2.5 mm, 0.45 mm pitch
One size up or down
- 3/16 BSWØ4.76 mm (up)
Got a bolt and no idea what it is? Measure the outside Ø and type it into Benchsmith → Find → Thread.