Morris Minor Owners Club

Could someone explain how whitworth sizes work!? They make no sense to me..what do they measure? Oh and if someone would be so kind as to explain different threads that would be nice, I'd like know what UNF and BSF mean.

A long time ago every nut, bolt and thread was made to whatever size someone felt like making. This was a real problem so some decent engineers set about defining good standards for threads and hex sizes.
One of the best thread standards was the Whitworth spec, and this was used widely in the UK car industry for a while. The American?? UNC/UNF thread standards became more prevalent around the world (C - course / F - fine pitch) and was also used in the UK and whitworth died out.

Nowadays pretty much everything in Europe has gone Metric and the Yanks are following slowly.

The whitworth standard was based on best engineering practice - ie to specify the bolt by it's thread diameter, and have a standard hex size for it. Therefore the hex size is denoted by the thread, not the 'across flats' measured size. This seems odd if you are used to using the 'across flats' measurement but for whichever you normally use, after a while you know which spanner/socket is needed just at a glance without having to measure anything.
Choosing the right tool is much more difficult on a car that has a mixture of many types!!

Metric threads do of couse have a 'standard' hex size which was chosen as a nice round number in metric, not neccessarily the optimum size. The advantage is that the hex size 'in theory' will relate to a standard hex bar size but in practice, bolts are not made from hex bar anyway. An 18mm hex will of course use a 18mm spanner, but from the spanner size you can't neccessarily work backwards to know what thread is used as the auto industry uses a bit of artistic license when it comes to matching heads and threads - therefore you need to look in a manual to find torque settings, whereas with the old standards you could use experience.

i did wonder if it related to thread size, but the difference in hex size you find with the same thread size confused me. Thanks for that ray!

Hello MH,

there is a little more history to the confusing 1\16" difference between BSW and BSF. During the war and in order to save metal the head size of Whitworth fasteners was decreased to the next larger diameter. For instance after the metal saving, a 1\4" W spanner actual fits a 5\16" fastener. Quite how the BSF sizes were that way I can't say but you will be unlikely to come across any pre war fasteners now.
When I did my apprenticeship in the mid sixties at an old Power Station the mix of head sizes was quite common which was confusing to say the least.

Alec

Alec wrote:Hello MH,

-snip- but you will be unlikely to come across any pre war fasteners now.
-snip-
Alec

unless working on a pre- war car, of course! ( last year I nearly went to have a look at a 1932 Aunstin Nippy resto project).

There's a couple of other differences too, although these have nothing to do with the spanner you use. The form of the thread differs between the systems. I can't remember the values, (my metalwork exam was a good few years ago) but the angles of the faces on the thread, and the shape of the thread peak and thread root are defined, and are different.

I was told UNC/UNF were American, too so that agrees with what Ray was thinking. I was told the were Unified National Coarse / Fine.

Yes - the thread design (profile and angles) are different between most of the standards so even if it has the same TPI (threads per inch) it may not be the 'ideal' nut for a bolt.

I only left a simplified history (partly on purpose) - but yes BSW and BSF use the same spanner range but for different thread diameters due to the war effort and need to save metal!
AFAIK the Whitworth thread form was the best of all the standards, however in modern life a common standard is more important that a good one!

Hello Ray,

yes, but of course, Whitworth was a common standard until others decided to make their own 'standard'.

Alec

I've just found an old spanner that must have been my grandad's, it shows the size as WW1/2 and BSF 7/16!

As far as threads go, would moggy threads be the american UNC UNF sizes?

As far as threads go, would moggy threads be the american UNC UNF sizes?

It really depends on the age of the car! On a series II they will be mainly Whitworth threads and on a late 60's car most of it would be UNC

Well mine is a 1970, cheers everyone, glad to have that cleared up!

Well mine is a 1970, cheers everyone, glad to have that cleared up!

Ah, yes! The H-plate should have given that away
The most likely place that you'll find whitworth is the bolts for the seat u-clamps. these are 1/4" Whit (same as 5/16" BSF). Maybe also door hinge bolts to A-pillar? Wing bolts? Not much really.

Hello all,

I think the simple division is Whitworth for the body and UNF\UNC for the engine and transmisssion.

Alec

Ray and alec, I believe dampers use whitworth sizes, 1/4 for mounting bolts at the front and the filler and 3/8's for the bottom bolt. Also aren't the wheel nuts 3/8 ww? My 3/8's ww socket fits the wheel nuts better than anything else.

Also aren't the wheel nuts 3/8 ww?

I've always found an 18mm to be a good fit on the wheel nuts. There are some similar (non Minor) nuts that aren't approx 18mm but I've never had a problem with standard Minor ones.

minor_hickup wrote:Also aren't the wheel nuts 3/8 ww?

Yep.

Basically the bits that did not change during production (most suspension & body bits) are Whitworth and the others UNF/UNC as Alec says.

most suspension & body bits

ah -ok. I've never really studied them as until the last few years all my cars were late Minor 1000's

I have worked out that the lower trunnion pin is different between the early and late cars. [unless this is just be a case of all my later cars having aftermarket parts. Either way there are definately 2 different types of lower trunnion pivot pin, which I found out when I got a brand new trunnion that had no nuts and the original (series II) nuts were significantly different.
(served me right at the time when I bought the parts - Id said "not to worry about searching for the missing nuts" as the original nuts were in good order Sods law - it gets you every time ) ]

From that I thought (probably wrongly) that they updated the fixings for the front suspension parts sometime after SII.

What really bugs me is when they use metric sized nuts/bolts on things!

minor_hickup wrote:What really bugs me is when they use metric sized nuts/bolts on things!

Guilty as charged

Does it help that I have a late model car with a Whitworth bolt in it

By them I meant those who produce items for moggies, you're safe!