this is STOLEN TECH, something i found on the net some time ago. trying to find something worthwile that nobody else thought of for TW. and i know a good number of us have british bikes. here goes: wonder why the fractional sizes stamped on your Whitworth wrenches don’t match the size of an ordinary (US) spanner? Why use a fine vs. co**** thread? Read on. This is more than you probably ever wanted to know. But hey, this is the age of information glut. In the 19th Century every British factory which needed to bolt something to something else devised their own fasteners to do it. Clearly, this caused all sorts of compatibility problems. So, along came Mr. Whitworth (I forget his first name right now) who invented a standardized system of co**** threads (with 55 degree thread angle and rounded roots and crests). This standardization was a Good Thing. Along with his threads came heads for the bolts that were based on the length along the side of one flat, rather than across the flats. Hence, there is no simple fractional number for the length across the flats, which is why your American wrenches don't fit. The fractional number on your English wrenches refers to the diameter of the bolt (which is 1/4", 3/8" etc. just like in the U.S.); not to the distance across the flats (which ends up being various weird dimensions). Some years later the Brits decided they needed a finer pitch for some applications, so another thread series was introduced (same 55 degrees). They also decided that the heads were too big for the bolts, so for most applications they switched to using the next size smaller heads. Because of this, and to add one more bit of confusion to life, one manufacturer will mark a particular wrench (spanner) 3/8BS, while a different manufacturer will mark the same sized wrench 7/16W. They fit the same diameter bolt. The first thing any fledgling Brit biker learns is that his motorcycle has "Whitworth bolts." They think this is interesting, buy a set of Whitworth wrenches, discover these wrenches fit their bolts, and believe they now know everything they need to know about British fasteners. Unfortunately, at this point they know only enough to make themselves dangerous. Instead, what they should have said to themselves is Ohmygod, what other weird and incomprehensible things have the Brits done to the fasteners on my machine? The answer to this question is: British Standard Whitworth (BSW) These are the original, 19th Century, co****-threaded industrial bolts designed to hold locomotives together. Because of their co**** pitch, they are more prone to vibrating loose, so are little used on motorcycles. Except for threading into Aluminum (e.g. crankcase studs), where a co**** thread is less prone to stripping than a fine one. It turns out that, except for 1/2" (where the Brits use 12 tpi, and the Americans 13 tpi) the thread pitches are the same as for American Unified Co**** (UNC). However, the thread form is different; Whitworth = 55 degrees; UNC = 60 degrees. In spite of this, mismatched nuts and bolts mate nicely, so you're likely to find UNC bolts or studs where BSW should have been. British Standard Fine (BSF) A finer pitch series, ****ogous to the American Unified Fine (UNF), although (unlike the case of BSW/UNC) with none of the pitches in common with UNF. Many motorcycle manufacturers commonly used a lot of BSF threads. CEI (Cycle Engineers' Ins***ute) or BSC (British Standard Cycle) These are different names commonly used for the same threads. 60 degree thread angle, rather than the 55 degree of BSW and BSF. For sizes from 1/4" through 1/2" by far the most common are 26 tpi, although 24 tpi appear as well. most but by no means all, fasteners on post-War BSA's (through the late '60's, when it got more complicated) were CEI. Although the thread form and pitch is different, the head sizes on CEI-threaded fasteners use the same wrenches as BSW/BSF. British ***ociation (BA) 47-1/2 degree thread angle. This is a metric thread system devised by the British for small screws used in components like speedos. Not metric like you might expect, but with diameters determined by a factor proportional to a power of the logarithm to the base 10 of the thread pitch in millimeters. I couldn't possibly be making this up. Ah, the English. You'll find lots of BA threads on any British bike, but only for fasteners smaller than 1/4". BA fasteners have their own set of wrench sizes. Typically, a set of Whitworth sockets will include a 0BA (and maybe a 2BA….bigger number = smaller size) socket. British Standard Pipe (BSP) A tapered, self-sealing thread system used to seal fluids (interestingly, the US and the metric world standardized on the BSP system for threading all their pipes). UNF and UNC In the late 1960's, when even the U.S. was thinking of going metric, the giant BSA corporation decided it was finally time to s**** that old 19th Century Whitworth-based system, and switch to....yes, you guessed it, American. Since they had lots of money invested in tooling, the switch wasn't made suddenly (or completely), so bikes from the late '60's and later had a mix of all sorts of thread forms. Typically, engine internals (e.g. the thread on the end of a camshaft) stayed with whatever form it used to have, while simple fasteners (e.g. holding the fenders on) switched to UNF. None of the Above While the above systems account for well over 95% of all threads you'll ever run across on a British bike, some manufacturers—again BSA springs to mind, but others were guilty as well--couldn't restrain themselves from inventing a few oddball pitches of their own. This is why, when dealing with British bikes, you should ***ume nothing. You must have a pitch gauge and calipers.
Way too much time on their hands making a mess of something good, & too late to realise they had completely lost it & made a real mess of what they once had, & second time round trying to pick where they left off....which didn't work either because that was already messed up.....now i'm confused Good post by the way! Just putting a '50 A7 back together & replacing the cyl base nuts.....do you think i could lay my hands on cycle thread nuts.....got some in the end but what a struggle, half the places i asked looked at me like i was from outer space! & all the nut'n'bolts above the cyl are UNF/UNC. This particular bike has a pre-production engine built by Perkins, identified by a two piece cyl head & no rifles on the casing.
Interesting stuff, especially since I've owned MGs Triumphs, and several British Bicycles including a Raleigh 10speed that I still have (With a frame made in England, not China!) How come all the words blur into mush right around where it says 3/8BS? Have they gone to metric yet, or are some companies still using Whitworth? Oh, by the way, I have always just drilled out and retapped to American sizes when I had a Whitworth "situation"
Funny you should ask that, its mostly going metric now but the last 20 yrs saw a real mixture on production cars, had to try & remember what had what & where! the one that hung in there the longest was the battery terminals...for some strange reason, the only wrench/spanner that would fit was a 1/4W, a fraction larger than 13mm or 1/2AF.
And that is why older brit mechanics have Very,very big tool boxes. 32 Limey if you are stuck for 26tpi nuts try your local pushbike shop the older spindles used em. john.
That had crossed my mind & was my next port of call but the local cl***ic bike shop had some in the end, at least he knew where i was coming from. thanks anyway!
Whitworth is a thread form, not a bolt size. Whitworth threads are stronger because the roots and peaks are radiused, not a sharp V as in NF threads. Fewer stress risers. Still used in critical-strength situations in space, aircraft, race tech. SOME of us have never really accepted the US thread, formerly called the Sellers thread after the Franklin Ins***ute guy who drew it. Bottom line- Whitworth is more expensive to make, requires more precise tooling. NF/NC were and are cheap to roll. Whitworth is waaaaay TRAD
I saw what happened after a newbee A&P went after a Rolls Royce Merlin in a P-51 with the wrong style nuts and bolts...! After a few thousand dollars of replacement parts and a different A&P it was flying around like new! "Scary in the Airy"!
Whitworth,BSF,imperial and metric spanners or wrenches. There is a conversion chart for whitworth/BSF/imperial/metric sizes at the foot of this page.. Use the proper spanner,may the ghost of Sir Joseph Whitworth haunt you if you damage his nuts with pliers... Whitworth,BSF,metric and imperial spanners are different sizes,some might almost fit but with very few exceptions they are not interchangeable.Whitworth,BSF and BA spanners,sockets and other tools for your old British motorcycle or car.Burred and damaged fastenings spoil many a rebuilt cl***ic,theres no need when the correct spanners are still available. Whitworth...an early attempt to standardise threads and spanner sizes.The size of a whitworth spanner refers to the thread not the measurement of the bolt head.Phased out in the 60's officially no longer used after 1965,but some manufacturers carried on using it on some applications much later than this.If you are a cl***ic car enthusiast you'll come across Whit sooner or later..The thread is co****r than.... BSF...British Standard Fine another attempt at a standard.Whitworth spanners will also fit BSF nuts and bolts.. B.A. ..British ***ociation often encountered on older electrical items,especially magnetos and dynamos etc.BA spanners were numbered 0 to 11 the larger the number,the smaller the spanner..all gradually replaced by... A.F stands for across flats not American fine.The imperial measure of a open ended spanner or nut,bolt across opposing sides.So a 3/4 af spanners fits a nut which is 3/4 inch across,easy peasy.Threads can be UNF (fine) or UNC (co****) still relatively common on older vehicles but now being replaced by... Metric ..in a way the same thing a 19mm spanner fits a nut 19mm acoss,threads can be co**** or fine very modern,very boring.
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