Threads
BSW and BSF Whitworth threads: sizes and threads per inch
BSW (British Standard Whitworth) and BSF (British Standard Fine) are 55° inch threads with rounded crests and roots, defined in the UK by BS 84. Largely replaced by metric and Unified threads, they remain in use for older machinery, some construction hardware and trade fasteners in India, the UK and other Commonwealth markets.
Names by standard
Standards in each region
| Region | System | Designation | Norma | Match |
|---|---|---|---|---|
| USA | No US standard | 1/2 in BSWWhitworth threads are not standardised in the USA; the British standard is used where they are needed. | BS 84 | Same material |
| UK | BS Whitworth | 1/2 in BSW, 1/2 in BSFGoverning standard; covers BSW from 1/8 in to 6 in, BSF and related Whitworth-form series. BSW dates from 1841, BSF from 1908. | BS 84:2007 | Same material |
| EU | DIN (legacy) | W 1/2"Former German Whitworth thread standard, superseded by metric threads. No current EN or ISO standard covers BSW. | DIN 11 (withdrawn) | Same material |
| Índia | Trade usage (BS 84 sizes) | 1/2" BSWNo current Indian Standard for Whitworth threads was identified. IS 4218 metric threads are standard for new fasteners; BSW sizes persist in trade, construction hardware and older equipment. | BS 84 | Same material |
| Japan | Former JIS Whitworth | W1/2Whitworth threads were removed from JIS but W-marked parts are still sold for construction, electrical and plumbing hardware. | Withdrawn from JIS (reported 1968) | Same material |
Thread form
Geometria
- Thread angle
- 55°, symmetric (27.5° flanks)
- Crests and roots
- Rounded, radius about 0.137 × pitch
- Thread depth
- About 0.640 × pitch
- Pitch expressed as
- Threads per inch (TPI)
- Designation
- Diameter + series, e.g. 3/8 in BSW or 3/8 in BSF; Japan uses W3/8
- Related form
- BSP pipe threads use the same 55° Whitworth profile on different diameters
Size chart
Common sizes
| Tamanho | Major diameter (in) | Major diameter (mm) | BSW TPI | BSF TPI |
|---|---|---|---|---|
| 1/4 in | 0.250 | 6.350 | 20 | 26 |
| 5/16 in | 0.3125 | 7.938 | 18 | 22 |
| 3/8 in | 0.375 | 9.525 | 16 | 20 |
| 7/16 in | 0.4375 | 11.113 | 14 | 18 |
| 1/2 in | 0.500 | 12.700 | 12 | 16 |
| 9/16 in | 0.5625 | 14.288 | 12 | 16 |
| 5/8 in | 0.625 | 15.875 | 11 | 14 |
| 3/4 in | 0.750 | 19.050 | 10 | 12 |
| 7/8 in | 0.875 | 22.225 | 9 | 11 |
| 1 in | 1.000 | 25.400 | 8 | 10 |
BSW continues above 1 in (to 6 in) and below 1/4 in (from 1/8 in). Pitch in mm = 25.4 ÷ TPI, e.g. 1/2 in BSW = 2.117 mm.
In practice
Uses and compatibility
Where it is used
- Replacement fasteners for older British, Indian and Commonwealth machinery
- Construction and fabrication hardware sold in inch sizes in India
- Tripod and camera mounts (1/4 in-20 and 3/8 in-16 Whitworth)
- Vintage vehicle and machine restoration
What interchanges
- BSW and BSF of the same diameter do not mate; the pitches differ at every size in the table.
- BSW and UNC share TPI at several sizes (1/4, 5/16, 3/8, 7/16, 9/16, 5/8, 3/4, 7/8 and 1 in) but not at 1/2 in (12 vs 13). The 55° and 60° forms do not seat correctly, so substitution reduces strength and is not recommended.
- BSF does not match UNF at the common sizes (e.g. 1/4 in BSF 26 TPI vs UNF 28 TPI).
- BSW and BSP share the 55° form, but a 1/4 BSP pipe thread is about 13.2 mm in diameter, not 1/4 in. They are different series.
- Whitworth threads do not interchange with metric threads.
Perguntas respondidas
Common questions
What is the thread angle of BSW?
BSW and BSF use a 55° thread angle with rounded crests and roots. Unified and metric threads use 60°.
Is 1/2 BSW the same as 1/2 UNC?
No. 1/2 in BSW has 12 threads per inch and 1/2 in UNC has 13, and the thread angles differ (55° vs 60°).
Is BSW still used in India?
Yes, in trade and older equipment. New Indian fastener standards use IS 4218 metric threads, but BSW sizes remain common for construction hardware, replacements and some general fasteners.
What is the difference between BSW and BSF?
Both use the 55° Whitworth form. BSF has more threads per inch and a shallower thread for the same diameter, for example 3/8 in BSF has 20 TPI against 16 for BSW.
From the Corona catalog
Products listed with BSW / BSF
Barras roscadas
Diâmetro: 1/4-2 1/2 in / M6-M60 · Comprimento: 3-20 ft / 1-6 m
Especificações
Tirantes (rosca nas duas extremidades)
Diâmetro: 1/2-2 1/2 in / M12-M60 · Comprimento: 3-20 ft / 1-6 m
Especificações
Barras roscadas
Diâmetro: 1/4" - 2-1/2" / M6 - M60 · Comprimento: 2 ft - 19 ft (3, 6, 10, 12 ft comuns) / 1 m - 5,8 m (1, 2, 3 m comuns)
EspecificaçõesKeep reading
Related references
References
Sources
- British Standard Whitworth (Wikipedia) — BSW TPI, major diameters, 55° profile, radius and depth factors.
- British Standard Fine (Wikipedia) — BSF TPI and 1908 introduction.
- BSI: BS 84:2007 Parallel screw threads of Whitworth form — Scope and current status.
- MISUMI: Whitworth screws (withdrawn from JIS, still used in Japan)
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.