When everything seems to be made of different threads in both imperial and metric in my car, Is there a tool which can tell you what thread something is, and what pitch the thread is.

I'm thinking for things like brake fittings etc. its the kind of thing i really don't to get wrong as it could work out REAL expensive

Yup...a thread gauge...

A bit like a penknife with lots of blades...each blade has a different thread pitch on (inch or metric)...you just see which blade fits your bolt/screw...and it's obvious when you have the right one.

HTH,

Alan

like this...

[Edited on 16/10/07 by Alan B]

A thread gauge is probably the most accurate option, although simply measuring across the top of the threads gives you the pitch

Cheers

Alex

Alan beat me to it

[Edited on 16/10/07 by ecosse]

you can get them on ebay for around £3

Item number: 220160285283

ah nice one! thought there had to be an easy way

cheers guys!

I'm starting to get round to sorting out some braking, and really didn't want to end up with the wrong fittings since it'll all be a mixture of manufacturers, vauxhall, ford, willwood, and girling... could be a nightmare, but i'll get me one of those thread gauge thingys

A thread guage will only tell you the pitch, to work out the nominal thread type you need to involve some simple maths.

Measure the inside bore - providing the thread is 100% thread form (which to be honest most are not) - if imperial multiply the pitch x 0.64 this is the depth of thread. Multiply by 2 and add this to the core diameter you just measured. For ISO (Metric) threads the formulae is 0.6.

For male threads simply minus the 2 x depth of threads from the major diameter to achieve the core diameter.

It's only a guide but it works...

Steve

And don't get your UNC mixed up with your Whitworth.

I found that 1 set of '60 degree metric' and 1 set of 'American national' thread gauges serve me for all the jobs on my car. The titles sound grand, but the first covers all standard metric threads you're likely to encounter on a car (coarse and fine), and the second covers all the UNC and UNF threads you'll find on an older Ford engine like my x-flow.

Combine these with an accurate way of measuring the thread diameter* and you can work out just about all threads you'll encounter in a car build. You can even use the imperial one to guess at a BSW or BSF thread - you can identify the pitch, but the gauge won't fit the thread properly (BSW and BSF are 55 degree threads, IIRC). I haven't got a single one of those on my car though.

David

* When measuring a thread diameter, remember that it will ALWAYS be a bit smaller than the declared size!

quote:

---

Originally posted by blakep82
ah nice one! thought there had to be an easy way

cheers guys!

I'm starting to get round to sorting out some braking, and really didn't want to end up with the wrong fittings since it'll all be a mixture of manufacturers, vauxhall, ford, willwood, and girling... could be a nightmare, but i'll get me one of those thread gauge thingys

---

5/16" UNC and M8 are the usual culprits - you can wind one onto the other for about 3/4 of a turn. If you don't realise what you've done and keep winding, you knacker one or both of the threads!

To add to the advice so far, a 'Zeus' book is a very useful aid to someone dealing with various unknown threads, plus a thread gauge and a digital caliper.

The Zeus book will also give you the size of tapping drills, which might be handy

ok, i measure the inside of the theaded hole on my calipers, came to just a tiny tiny bit under 3/8" (9mm, so faily sure its not metric)

now, since the uprights are from a bedford midi van (also isuzu and something else) is it going to be 3/8" thread? i really want to order some brake parts since i'm off work next week. want to get something mechanical working