Looking to buy Whitworth or BSF bolts that no stockist carries? This page covers the thread data for BSW, BSF and BA, the sizes you can still buy off the shelf versus the ones you can't — and how to have the missing ones made to your sample, photo or hand drawing.
The Whitworth Problem in 2026: The Threads Outlived Their Supply
British Standard Whitworth (BSW) held British machinery together for over a century, with BSF as its fine-pitch partner and BA covering instruments and electrics. The machines are still here — pre-war cars, classic motorcycles, machine tools, traction engines, pumps and plant — but the fastener supply is not. Major manufacturers have discontinued whole BSF ranges, and stockists openly describe these threads as end-of-line.
What remains in stock is the easy middle: common hex setscrews in common lengths. Step outside that — an odd length, a larger diameter, a square or cheese head, a stud, a castle nut, stainless steel — and the answer everywhere is the same: obsolete, no longer available.
EKINSUN machines those missing fasteners to order, in the correct 55° Whitworth form, from whatever you have: the worn original, a photo with one measurement, or a hand-drawn sketch. No CAD file, no minimum batch.
Whitworth (BSW) Thread Data
BSW is the coarse series: 55° flank angle, rounded roots and crests, standardised by Joseph Whitworth in 1841. Diameters and threads per inch for the common range:
| Nominal size | TPI (BSW) | Nominal size | TPI (BSW) |
|---|---|---|---|
| 1/8" | 40 | 1/2" | 12 |
| 3/16" | 24 | 9/16" | 12 |
| 1/4" | 20 | 5/8" | 11 |
| 5/16" | 18 | 3/4" | 10 |
| 3/8" | 16 | 7/8" | 9 |
| 7/16" | 14 | 1" | 8 |
BSF Thread Data
British Standard Fine — same 55° Whitworth form, finer pitches. The standard automotive and engineering thread of pre-1950s Britain, and the one hardest hit by discontinued stock ranges:
| Nominal size | TPI (BSF) | Nominal size | TPI (BSF) |
|---|---|---|---|
| 1/4" | 26 | 9/16" | 16 |
| 5/16" | 22 | 5/8" | 14 |
| 3/8" | 20 | 3/4" | 12 |
| 7/16" | 18 | 7/8" | 11 |
| 1/2" | 16 | 1" | 10 |
BA — the small stuff
British Association threads cover instruments, magnetos, carburettors and electrics. BA is metric-based with a 47.5° form; sizes run 0BA (6.0 mm × 1.0 mm pitch) down through 2BA (4.7 mm × 0.81), 4BA (3.6 mm × 0.66) and 6BA (2.8 mm × 0.53) to smaller. We cut BA alongside BSW/BSF, and also CEI/BSC 26 TPI "Cycle" threads for classic motorcycles.
The Whitworth vs UNC trap. On most sizes BSW and American UNC share the same TPI — but the forms differ (55° rounded vs 60° flat) and at 1/2" they don't even share a count: BSW is 12 TPI, UNC is 13. A UNC bolt will often start in a Whitworth hole, bear only on partial flanks, and strip the thread in a casting you cannot replace. If the joint matters, fit the correct form.
What We Make That Stock Ranges Don't Cover
Odd lengths & diameters
Any length under or over the catalogue range, including large BSW above 1".
Period-correct heads
Square, cheese, slotted, domed and radius-end pre-war profiles — not just modern hex.
Studs & setscrews
Plain, waisted or stepped studs; BSW one end, BSF or metric the other.
Nuts to match
Full, thin, castle and slotted nuts in BSW/BSF/BA, standard or period hexagon sizes.
Stainless upgrades
A2/A4 stainless in threads only ever sold in plain steel.
One-off specials
Banjo bolts, shouldered bolts, tapped bosses — anything threaded 55°.
Materials: EN8, EN16, EN24T steels · A2 (304) / A4 (316) stainless · brass · bronze. Finishes: plain, black oxide, zinc — chosen for period authenticity or corrosion resistance. If you need something harder or stranger, ask; see also our non-standard thread bolts for odd pitches outside the British families.
Three Ways to Order — No CAD Needed
1 · Post a sample
One original, even worn or rusty. We gauge thread, head and length, and restore worn features to design intent.
2 · Photos + one size
Sharp photos, one measured dimension, and a thread count against a ruler. Enough to identify most threads remotely.
3 · Hand drawing
A dimensioned sketch on paper. We redraw it in CAD and confirm the callout with you before cutting.
Whichever route you use, thread identification is free with the quote, the CAD we build is kept on file for instant reorders, and the drawing is yours to approve before we machine. The full process is described under reverse engineering and in our guide to identifying an unknown thread.
Who Orders These
- Classic car & motorcycle restorers — pre-war and post-war British marques where BSF is everywhere and originality matters. See our note on restoring vintage machinery parts.
- Machine tool & workshop rebuilders — lathes, mills and presses whose castings are tapped Whitworth and must never be re-tapped oversize.
- Steam, traction engine & heritage rail volunteers — large BSW in odd lengths, often in small matched sets.
- Plant & pump maintenance engineers — old installed equipment that still earns its keep and just needs the right bolt.
A note on branded parts. We machine compatible fasteners to the original's form, fit and function from your sample or drawing. We don't sell branded originals or imply any affiliation with the original manufacturer.
Frequently Asked Questions
No. Pitches match on most sizes, but Whitworth is a 55° rounded form and UNC is 60° — and at 1/2" the counts differ (BSW 12 TPI vs UNC 13). A UNC bolt may start in a Whitworth hole but bears incorrectly and can strip a vintage casting. Fit the correct form where the joint matters.
Yes — that's the core of this service. Odd lengths, big diameters, studs, square/cheese/domed heads, castle and slotted nuts, and stainless versions of sizes only ever sold in steel.
Yes, free with the quote. Post the sample and we gauge it; or send sharp photos, one measured dimension and a thread count against a ruler and we can usually identify it remotely.
Yes. A dimensioned hand sketch is enough — we redraw it in CAD, confirm the thread callout with you before machining, and keep the file for reorders.
One piece. There's no tooling charge on machined fasteners; unit price drops from about 3–10 pieces as setup is shared, with all tiers quoted upfront.
Yes — A2 (304) and A4 (316), plus EN8/EN16/EN24T steels, brass and bronze, with plain, black-oxide or zinc finishes for period-correct work.
Quote in 24 hours; typically 7–12 working days machining after drawing approval, plus tracked worldwide shipping. Rush jobs — tell us, small batches can often be expedited.
Get Your Whitworth / BSF Fastener Made
Send a sample, photos or a sketch — thread identification is free with your quote.
// Qty & price
1 pc
Sample price
Confirm fit before a run
3–10
Unit price drops
Setup cost shared
10+
Best price
All tiers quoted upfront
- →No distributor — you pay the maker directly
- →CAD saved after first order — reorder anytime at lower unit price