Whitworth bolt's head size

[Rogerfrench]

 As Holmes once remarked to Watson "That man owns a 2CV" "Why, how do you know that Holmes?" "I note an M7 spanner in his tool box."

Holmes always was a smart-arse, making guesses based on incomplete evidence.

He could have owned a Bugatti.

Charles

Or a Lotus Europa, or again the Renault from which its gearbox was borrowed.

[Cliff Ringrose]

What a great thread (pun intended) this has been. I hapily stand corected on my 1951 text book quote. I could only find two proper old Whit. bolts, one 3/8" and one 1/2", and in neither case did the across flats formula work, nor were the across points 2Dia, the smaller one slightly less, the larger slightly more. I have however a foolproof way of remembering which have a 55 degree angle, and which a 60. Any fool can construct a 60 degree angle, so that is the one chosen by those metric continentals and the unified colonials, only the Brits. use a sensible 55!
Cliff.

[Paul N-M]

This is just what I was hoping for.
Like Paul N-M I wonder where else on the interweb such informed opinions would be offered.
I believe that the diameter across the points, the length of the flats and the distance across the flats (AF) are all simply related to each other and aren't related linearly to the shank diameter in Whitworth bolts. Like Cliff Ringrose I have read that the diameter across the points is twice the shank diameter, but I am pretty sure that this isn't true.
I have tested the formulae offered and, within the limits of my calculator skills, I think Colin Morgan's 1.5 x Shank diameter + 0.16" gives good results.
I have seen it suggested that the head diameters were specified because there was hex-bar available in an approximately suitable size, so that the head dimensions are basically due to chance. Colin's formula would suggest that this isn't the case.

A detailed and amusing description of various systems of fasteners from an American perspective is on the "Progress is fine but it has gone on too long" web site.

Joseph Whitworth produced the specifications for the Whitworth thread in 1841, but I can't see where he worked out head sizes for bolts.
By the start of last century a finer thread was needed for steel (rather than cast iron) fasteners and so BSF was introduced. With a head size one size smaller than Whitworth. In the 1920s Auto-whit, Whitworth with smaller head-size, steel bolts began to be used in some cars. In the early years of WWII it was decided to reduce the head size of all Whitworth bolts to that of the BSF bolts of the same shank diameter in order to save metal - the bolts could be produced from smaller hex-bar. The new Whitworth bolts were called BSW. The same spanner will fit both BSF and BSW bolts of the same shank diameter and are often marked just BS.

This would explain why old inherited W spanners mixed in with later BSW & BSF dont fit!!!!!! I had to go through the BS tray and take them all out. Though they still get used for some fittings.

[Bob Culver]

A school colleague's father was an old world class conscious very proud Pom worker who had spent time in a workshop. He reckoned the only virtue of the then American AF hardware (SAE,UNF) was that the nuts could be easily split off with a chisel!* It is notable that the standard metric threads closely approach BSF in proportions. From a 1920s book seems BSF was first proposed in 1905. Many cars had their own threads prior. 

Quite a few publications have a table of all the various threads and pitches and tapping sizes in progression. These charts are very useful for identification and for remedy work, esp where not too critical.Over short lengths can get by with slight pitch differences.

The table of spanner openings appeared in many Haynes manuals. Handy for selecting a socket which can be tapped onto manifold nuts etc on other makes corroded smaller and otherwise damged.

* he also reckoned the only virtue of American raised v lathe beds was tht workers  could not sit on them.

[Steve kay]

   

And talking of nuts and bolts.....

Immediately before Xmas I was in Mrs Watkins in Hereford stocking up on obscure fastenings when a new range of eye bolts caught my notice. I had been browsing in chandlers for suitable eye bolts to make up head/engine lifters, using the spark plug extensions discussed in the esteemed forum in the past, but without success. These looked perfect, and with just a quick brush from a reamer fitted into the extension, as illustrated.  The debate on threads etc might have attracted the attention of experts who might comment on whether one nut at the bottom of the 8mm eyebolt will be strong enough for engine lifting.  Would a second nut be necessary for strength, though obviously not needed as a lock nut. The threaded end will be shortened as required.  There would of course be two of these lifting aids.

The mention of lock nuts might stir the memories of more senior forumists, when the correspondence pages and articles of Tubal Cain in the Model Engineer were torn by vigorous debate as the whether half lock nuts were desirable, should be inside or outside the main nut, whether lock nuts were necessary, and whether nylock nuts were a modern threat to civilisation.

[Colin Wilks]

I suspect an engineer would say "It all depends". Best to check your nuts!

  A short guide to metric nuts and bolts.pdf (Size: 289.29 KB / Downloads: 11)

Happy new year.

[Tony Press]

"Would a second nut be necessary for strength, though obviously not needed as a lock nut. The threaded end will be shortened as required."

Careful to be clear of the piston crown !

[Zetomagneto]

Its not so much the nut you need to be concerned about, the 8 mm threaded section will be in tension, what is it’s tensile strenght? thats what you need to know. I would not suspend my engine on a single 8 mm bolt of unknown data.

[Bob Culver]

Mild steel is at least 20 tons per square inch, common ht about 45. 
Allowance has to be made for indirect tug, jerks etc but the core, more than 1/4 inch dia, is more than 1/20 square inch. Bolts usually fail before the thread pulls out.

[Steve kay]

The stainless eyebolts are intended for boats' rigging, and when I find the spec I hope that they are strong enough to avoid masts falling over, and so easily support Seven engines. The wondering about nut capacity was indeed because a single nut is happy in the cavernous combustion chamber, whereas with two piston height must be taken seriously. Considering how often heads and engines are lifted it should not be difficult to be scrupulously careful about where the pistons are in nos 1 and 4 cylinders. Thanks as ever to forum contrinbutors.