KEVOS® MAKEOS · Threads
Whitworth Thread Basic Dimensions
What are the basic pitch and minor diameters of this BSW, BSF or BSP (parallel) Whitworth thread?
Basic depth, pitch and minor diameters and crest/root radius of a 55° Whitworth form thread (BSW, BSF, BSP parallel) from its major diameter and threads per inch.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Major diameter | in | Basic major diameter in inches (BSP sizes use the pipe thread outside diameter, e.g. 0.825 in for ½ BSP). |
| Threads per inch | TPI | Threads per inch (e.g. 12 for ½ BSW, 14 for ½ BSP). |
Method and formulas
- Fundamental triangle H = 0.960491p; depth h = 0.640327p; radius r = 0.137329p (p = 1/n).
- Pitch diameter = D − h; minor diameter = D − 2h.
- Example: ½ BSW (12 TPI) has a pitch diameter of 0.44664 in and a minor diameter of 0.39328 in.
Limitations
- Basic dimensions; tolerances come from BS 84 (BSW/BSF) or ISO 228 (BSP parallel). BSPT is tapered and not covered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Repair and replace parts on older British equipment
- Inspect Whitworth form threads
- Convert Whitworth thread sizes to metric dimensions
Who it is for
- Maintenance fitters
- Machinists
- Quality inspectors
What you get
- Thread depth
- Basic pitch and minor diameters
- Crest and root radius
Interpreting the result
- Do not mix Whitworth (55°) and unified or metric (60°) threads; they look similar but do not fit properly.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1980–1989, 1995–1998. Topic reference; no source tables or recommended settings are reproduced.
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