1/8-28 BSP Thread Dimensions
1/8-28 BSP is a pipe British Standard Pipe (parallel) thread. There are 28 threads per inch on a 0.3831 in major diameter, giving a metric-equivalent pitch of 0.907 mm. The size label is a nominal bore rather than a diameter.
Thread profile
millimetres unless statedBasic information
- Designation
- 1/8-28 BSP
- Thread system
- British Standard Pipe (parallel)
- Series
- pipe
- Standard
- ISO 228-1
- Basic profile
- Whitworth basic profile
- Flank angle
- 55°
Dimensions
- Major diameter
- 0.3831 in / 9.73 mm
- Pitch (metric equivalent)
- 0.907 mm
- Threads per inch
- 28
- Pitch diameter
- 0.3602 in / 9.15 mm
- Minor diameter (external)
- 0.3374 in / 8.57 mm
- Minor diameter (internal)
- 0.3374 in / 8.57 mm
- Thread depth
- 0.0229 in / 0.581 mm
- Recommended tap drill
- Ø 0.3472 in / 8.82 mm
How these values are derived
tabulated standard valuesThis is a pipe thread, so the published dimensions are tabulated values from ISO 228-1 rather than figures derived from a formula: a pipe size is a nominal bore, and the relationship between that bore and the thread diameter is historical, not geometric. Diameters are quoted at the gauge plane; the thread itself is tapered, so the actual size changes along its length.
Compatible parts0 specification pages
No specification in this database uses 1/8-28 BSP. That is expected: the catalogue covers machine screws, bolts, nuts and washers, and pipe threads belong to fittings, which are a separate family of parts. The dimensions above are still the standard ones for the thread itself.
Related
Neighbouring sizes in British Standard Pipe (parallel).