imperial nuts n bolts??
Turbo Mini Forums

hey, what type of thread system iz used on mini's? When i got my car it woz diss-assembled and missing lots of bits n pieces including all the bolts that held it together, i live in Aus and woz braught up on the metric system so i dont know what guage thread i should be looking for?

Idno if that is going to make sence to every one else so if you need me to explain a bit better just ask.

Thanks. Chris

998 turbo

the finer thread is UNF

The coarse thread is WHITWORTH

measure the dia" and ask for the fastner in this size

its as simple as that!

sweeeeet, thanks

998 turbo

sorry but you have 5/16 unf (finer thread) 8 mm.
5/16 unc corse thread 8mm shaft (thereabouts).
3/8 unf and unc
also some smaller 1/4 unf threads eg heater tap bolts.

ben there is no whitworth old mate.

always looking for them bigger bunches of bannanas

ah mr hogster

i am enlightend! my friend

i have based my assumption on my memory
as from a number of years ago

and alsa its stuck there assuming whitworth!

at a glance unc and whit look very simlar!

i stand corrected old chap!

thanks

yes they do i got caught out on that not long, as i tried to clean a thread with a 3/8 whit and wondered why it wouldnt go,

always looking for them bigger bunches of bannanas

lol, ok, thanks

998 turbo

The only Whitworth you'll find on a mini is the carburetor spindle I recall!

Right, lets start at the beginning!
Thread forms are measured in OD (outside diameter) and Pitch.
On metric threads, the pitch is measured in mm and the measurement refers to the distance from the tip of one thread to the tip of the next along the axial length of the thread. This distance will be between 0.7 and 1.75 for most stuff you'll use on cars!
The 'pitch' of imperial threads is designated in 'TPI' (Teeth Per Inch). Basically, this means how many thread 'peaks' there are within a full one-inch length of thread. This will be between 13 and 28 for almost all the stuff on your mini.

So how do you tell which is which?
What you need to find my friend is a set of imperial thread gauges, a set of metric thread gauges and a digital caliper/micrometer. A thread gauge looks like this:
http://www.machinemart.co.uk/product.asp?p=060720157

You measure the diameter of the thread in mm (imperial micrometers are not something I can teach to read over the net*). Note down the size. Compare the diameter to those on the charts below. Bear in mind, threads will often be slightly under the stated size ? eg M8 will often be 7.8 to 7.9mm when measured across the diameter of the thread.

Let?s do an example: Say you find a bolt, and it measures 7.9mm OD.
As mentioned earlier, most M8 bolts will measure just under 8mm, so in theory this could be 5/16 (UNC or UNF) or 8mm; so you have to do a little investigative work.

Firstly, clean the thread with a wire brush. Now take the metric gauges and try to find the best fitting gauge that neatly sits into the thread form. The correct one will sit EXACTLY into the thread form, with no daylight visible when you hold the bolt and gauge up to the light. Note what the gauge 'number' is.
Now repeat the same with the Imperial gauges, again noting the gauge number.

In doing this, you'll be left with one metric or one imperial gauge that fitted better than the other. The correct thread will be obvious.
Now all you do is compare your findings to the tables below?
For example;
We already know the OD is 7.9mm, but the pitch gauge that matched was 18tpi, hence this thread was 5/18UNC

Easy Peasy ? but only once you?ve been taught!


* anyone who?s been taught and used an imperial micrometer will know exactly what I mean!

Just made another copy of this into the 'knowledge' section... Usefull for the future I reckon!

wow...

I didn't know there was that much to it!!

Alex

AlexF

thought you were an engineer alex....

i knew that lot an im only a youngster in the engineering world!

Learnt all this exciting stuff doing ONC when I was a mere 16! (although my father had shown me how to measure threads well before that - but I never did get my head round the imperial mic until having it drilled into me head on't ONC)!

Another little gem on threads: the Whitworth thread form is by far the most superior thread form, thanks to its rolled root and crest radius and the 55 degree form angle (metric and unified are 60degree).

Don't know where it went wrong for Whitworth's populatiry however... Anyone know or is it 'Google time'?


Every 'self respecting' engineer will / should have at least one copy of this book! I've got one in my work desk, another in my workshop. It's laminted so oil/grease/tea just wipe off, and it was orignally written over 50 (!) years ago, so has no errors, and no un-neccesary bullsh1t!

Edited by turbodave16v on 21st Mar, 2005.

got one of those in my toolbox, cracking bit of kit

just seen one on ebay for ?4.50 with a quid P&P!

That is a bargain! WHsmiths used to sell them for ?7.50

On 21/03/2005 19:29:30 iain said:

thought you were an engineer alex....

i knew that lot an im only a youngster in the engineering world!

AlexF

I?ve been tightening nuts and bolts for over 30 years,

But after a while with that experience

I make just assumptions, With a glance

It?s all coarse metric these days!

Extremely concise Dave,

just been into the garage and raked out one of my old ones

Edited by BENROSS on 22nd Mar, 2005.

Assumptions are the beginning of the mother of all fu**ups!

Ben, you ever heard of re-sizing you pics? I know you want it to be seen but come on... !!@!@!

I did physics at Uni... then an HND in auto eng...

Sadly nither covered any machine shop... although the HND did teach welding!

Generally all qualifications are de-skilling thou :(

What apprenticeship did you do Iain?

Alex

AlexF

Yeah thats all i meant by it, nothing personal but you can see my point about the training being poor.

I did an AMA with siemens. Involved a NVQ2 with 13 units, welding, bench fitting, machining, CAD/CAM, CNC, Tech drawing, etc plus alongside i did a HNC (followed up with a HND) in mechanical engineering.
This was followed by a NVQ3 in design engineering.
First year was college full time ( a really good crack, being paid to be at college!!)
then the remaining training done in the workplace with day release for my HNC/HND.
Im starting a mech eng degree in september this year as its a requirement of the new job.
Still get full pay but only work 4days a week

wow, dats impressive, thanks for typing all dat up, hopefully i'll have it all down pat by the end of my build!

Thanks, chris

998 turbo

David, tried to resize it but to no avail

so its removed!

yes assumption is the mother of all,************

i will have to pull my socks up!

Ben... I'm about to tell some students that phrase in about 10 mins time!!

ITs a classic!

alex

AlexF

what happened to city guilds???????????

sorry city and guilds