How to identify a metric thread?

I want to replace some damaged bolts. I know they are metric thread, but don't know what size they are. What dimension do I need to measure to determine this please?
Thanks David
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Lobster wrote:

Measure the diameter of the bolt, to the outside of the thread. 10mm is M10.
--
Grunff

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Grunff wrote:

Thanks - looks like 4.5mm, which I don't believe! (don't have anything other than a ruler on me to measure it tho). I've just found a nut which matches it - this takes an 8mm spanner. That should define a specific thread size too, shouldn't it?
Thanks David
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Lobster wrote:

Most likely M5.

No, it doesn't define it - it just hints at it :-)
You can have different head sizes for a given screw size. M5s commonly have 8mm heads, but not always.
--
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Lobster wrote:

4.5 mm is close enough to 5 mm to get it wrong. How certain are you that you have metric threads? At this difference, parallax errors are quite large. You might have a 5 mm thread, but are reading it a little too small at 4.5 mm.
Find a bolt that you are certain of its size and compare diam. and thread pitch, as someone else has mentioned.
4.8 mm is 3/16 of an inch and that is too close to 5 mm to be sure either way.
Dave

8 mm is the same as 5/16 th of an inch, so beware until you know what thread you are seeing.
Dave
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|Lobster wrote: |> I want to replace some damaged bolts. I know they are metric thread, |> but don't know what size they are. What dimension do I need to measure |> to determine this please? | | |Measure the diameter of the bolt, to the outside of the thread. 10mm is M10.
Or a bit of undamaged shaft, 10mm is M10
It is also a good idea to get another bolt of the thread you thing it is, and check that the thread pitch is the same, by matching the two threads together.
############### \/\/\/\/\/\/\/\
\/\/\/\/\/\/\/\ ###############
Roughly like that, works OK even on mangled bolts
I have lots of Whitworth, Unified, BSF, BA etc. bolts which I keep in case I need them ?sometime?
--
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Dave Fawthrop wrote:

How is that different to measuring the outside of the thread?

If you're going to go getting, I'd rather get a nut and try it for size.
MBQ
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On 22 Mar 2006 07:36:33 -0800, snipped-for-privacy@hotmail.com wrote:
| |Dave Fawthrop wrote:
|> |> |Lobster wrote: |> |> I want to replace some damaged bolts. I know they are metric thread, |> |> but don't know what size they are. What dimension do I need to measure |> |> to determine this please? |> | |> | |> |Measure the diameter of the bolt, to the outside of the thread. 10mm is M10. |> |> Or a bit of undamaged shaft, 10mm is M10 | |How is that different to measuring the outside of the thread?
All of the thread may be damaged and be less than nominal.
|> It is also a good idea to get another bolt of the thread you thing it is, |> and check that the thread pitch is the same, by matching the two threads |> together. | |If you're going to go getting, I'd rather get a nut and try it for |size.
Nut may not may not run down damaged thread.
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On Wed, 22 Mar 2006 15:24:24 +0000, Dave Fawthrop

Foolish boy, everyone knows the keeping of such bolts is to ward off the need for them. If you have them you will never need them, if you don't you certainly will.
--
Peter Parry.
http://www.wpp.ltd.uk/
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Only on cut threads. Rolled threads will be about 9mm for a 10mm thread.
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Skipweasel
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| |> |Measure the diameter of the bolt, to the outside of the thread. 10mm |> is M10. | |> Or a bit of undamaged shaft, 10mm is M10 | |Only on cut threads. Rolled threads will be about 9mm for a 10mm thread.
I just thought of that as well, so a bolt with a thoroughly mashed up rolled thread is difficult to identify.
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Still reckon the best way is to take it to a shop and mesh threads with other bolts till you find a match.
Or, better yet, an industrial fastener specialist. There's one in most towns if you know where to look.
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| |> |Only on cut threads. Rolled threads will be about 9mm for a 10mm thread. | | |> I just thought of that as well, so a bolt with a thoroughly mashed up |> rolled thread is difficult to identify. | |Still reckon the best way is to take it to a shop and mesh threads with |other bolts till you find a match. | |Or, better yet, an industrial fastener specialist. There's one in most |towns if you know where to look.
Ours local Bolt and Nut specialist is *very* amiable
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On Wed, 22 Mar 2006 19:17:43 +0000, Dave Fawthrop

Our local Industrial Fastener Specialist <I.F.S.> is very expensive.
Best go there and get them to identify the thread and order the screws from Maplin/Farnells/RS etc.
DG
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wrote:
|On Wed, 22 Mar 2006 19:17:43 +0000, Dave Fawthrop
|
|>
|>| |>|> |Only on cut threads. Rolled threads will be about 9mm for a 10mm thread. |>| |>| |>|> I just thought of that as well, so a bolt with a thoroughly mashed up |>|> rolled thread is difficult to identify. |>| |>|Still reckon the best way is to take it to a shop and mesh threads with |>|other bolts till you find a match. |>| |>|Or, better yet, an industrial fastener specialist. There's one in most |>|towns if you know where to look. |> |>Our local Bolt and Nut specialist is *very* amiable | |Our local Industrial Fastener Specialist <I.F.S.> is very expensive.
Ours Bradford Bolt and Nut has a *huge* range of fastenings, and tools, many times that of the sheds. All competively priced. | |Best go there and get them to identify the thread and order the screws |from Maplin/Farnells/RS etc.
The Bradford Maplins is now very poor. Haven't used Farnell for years.
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Sadly they all are. They've gone the way of Halfords - bling and toys.
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Guy King wrote:

Sad indeed..
I called into the Manchester branch the other day to find they didn't even have a component counter! If I wanted any resistors etc I'd have to order them!
The place seemed more like a small branch of Toys 'R Us.
Mathew
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Given that all 'shop' suppliers of electronic components have also disappeared it's not surprising. It's sad, but home construction of electronic things is no longer popular as a hobby. Maplin have high cost high street shops and can't afford to stock low moving products in them.
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Which will make IFS even more expensive. What you are suggesting is immoral. Taking advantage of a supplier who provides a service, with no intention of purchasing from them. When the IFSs of this world have all closed, you will be whining that there is nowhere to go that has a clue.
--
AJL

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On Thu, 23 Mar 2006 10:18:44 +0000, "Andy Luckman (AJL Electronics)"

They weren't competetive.

FWIR the price of the screws at IFS was about 3-4 times the price in B&Q (It was in the days when you used to weigh them out yourself).
So they only got my business *once*.
AAMOF, I was expecting a specialist supplier to be significantly cheaper than B&Q.
DG
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