1-1/4-11 BSPT taper Thread Dimensions
1-1/4-11 BSPT is a pipe British Standard Pipe (taper) thread. There are 11 threads per inch on a 1.65 in major diameter, giving a metric-equivalent pitch of 2.309 mm. The size label is a nominal bore rather than a diameter.
Note. Diameters are quoted at the gauge plane. The thread is tapered 1:16 on diameter, so the actual size changes along the thread.
Thread profile
millimetres unless statedBasic information
- Designation
- 1-1/4-11 BSPT
- Thread system
- British Standard Pipe (taper)
- Series
- pipe
- Standard
- ISO 7-1
- Basic profile
- Whitworth basic profile
- Flank angle
- 55°
Dimensions
- Major diameter
- 1.65 in / 41.91 mm
- Pitch (metric equivalent)
- 2.309 mm
- Threads per inch
- 11
- Pitch diameter
- 1.5917 in / 40.43 mm
- Minor diameter (external)
- 1.5335 in / 38.95 mm
- Minor diameter (internal)
- 1.5335 in / 38.95 mm
- Thread depth
- 0.0582 in / 1.479 mm
- Recommended tap drill
- Not applicable — see note
How these values are derived
tabulated standard valuesThis is a pipe thread, so the published dimensions are tabulated values from ISO 7-1 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 1-1/4-11 BSPT taper. 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 (taper).