RE: [CR]Witworth tools for British Bikes

Thanks, that is enlightening. Does this mean that the "English" threads on bicycles since WWII have been BSC and that those bolt heads that are not metric will require Whitworth wrenches? The fasteners on my circa 1974 Lambert are clearly not metric and generally require an English wrench (though often xx/32). Are these really BSC fasteners for which the proper tools would be Whitworth ones? Does this mean the wrenchs that we are used to calling "English" are actually "American" and were never actually used in England except by those who owned American cars? Did Raleigh and the other large English manufacturers continue to use Whitworth-head fasteners after WWII, and if so, for how long? What standard did the US bike manufacturers use before they adopted metric-head fasteners? What did the English manufacturers do when a bike had a mix of English, French, and Italian components? Did the buyer have to buy both metric and Whitworth tool sets?

This is a lot of questions, but I have just discoverd the depth of my own ignorance about bicycle threads. And to think I considered myself knowledgeable for knowing the difference between English, French, Italian, ans Swiss threading.

Regards,

Jerry Moos

-----Original Message----- From: Aldo Ross [mailto:swampmtn@siscom.net] Sent: Friday, June 22, 2001 1:43 PM To: Classicrendezvous@bikelist.org Subject: Re: [CR]Witworth tools for British Bikes

Joseph Whitworth was the designer of screw threads. Beginning in the 1840s, he introduced tools and methods to allow a uniform system ot threads to be developed, leading eventually to the BSW (British Standard Whitworth).

Within the Whitworth system, the width heads (across the flats) and the corresponding wrenches differ in size from those of the American National Standard, i.e. an ANS 1/2" heavy hex head bolt is 7/8" or less acrss the flats, an ANS 1/2" (regular duty) hex head bolt is 3/4" or less across the flats, and a BSW is 13/16" or more across the flats... the "or more" is important, as the head dimensions on ANS bolts are a bit smaller than those in BSW, so the BSW require a slightly larger opening in the wrench.

I found this better explanation on the web:

First, a tiny bit of history. 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 coarse 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 imperial spanners don't fit. The fractional number on your spanners refers to the diameter of the bolt which is 1/4", 3/8" etc. not the distance across the flats (which ends up being various weird dimensions). Some years later the British decided they needed a finer pitch for some applications, so another thread series was introduced (same 55 degree angle). 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 spanner "3/8BS," while a different manufacturer will mark the same sized spanner "7/16W." They fit the same diameter bolt. The first thing any fledgling British car restorer learns is that his (or her) car has "Whitworth bolts." They think this is interesting, buy a set of "Whitworth spanners," discover these spanners 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 "Oh my God, what other weird and incomprehensible things have they done to the fasteners on my machine?" The answer to this question is:

British Standard Whitworth (BSW)

These are the original, 19th Century, coarse-threaded industrial bolts designed to hold locomotives together. Because of their coarse pitch, they are more prone to vibrating loose, so are little used on motorcars. Except for threading into aluminum (e.g. crankcase studs), where a coarse thread is less prone to stripping than a fine one. It turns out that, except for 1/2" (where the British use 12 threads per inch (tpi) and Americans use 13 tpi) the thread pitches for the rest are the same as for American Unified Coarse (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, analogous to the American Unified Fine (UNF), although - unlike the case of BSW/UNC - with none of the pitches in common with UNF. Many motorcar and motorcycle manufacturers commonly used a lot of BSF threads. Cycle Engineers' Institute (CEI) or British Standard Cycle (BSC)

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 CBI-threaded fasteners use the same wrenches as BSW/BSF. British Association (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 car, but only for fasteners smaller than 1/4". BA fasteners have their own set of spanner sizes. Typically, a set of "Whitworth" sockets will include a OBA (and maybe a 2BA--bigger number = smaller size) socket.

Aldo Ross