How to identify a metric thread?

[Dave]

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

[Dave]

In the year 2006 when was the last time you saw a cut thread?

I'll bet it was a long time ago.

Cutting a thread costs a lot more than rolling them.

Dave

[Nick]

I often need to identify threads, without even knowing whether they are metric or not. So I use this chart. The bit you want would be somewhere in the middle. The diameter is the width to the outside of the thread, and that may be slightly smaller than on the chart. Also count the distance that 10 threads take, to work out the pitch.

Type Size Dia Inch TPI Dia mm Pitch mm

BSW 5/32 0.15625 32 3.97 0.79 MF 4 0.157 50.80 4 0.5 M 4 0.157 36.29 4 0.7 BA 3 0.1614 34.84 4.10 0.73 M 4.5 0.177 33.87 4.5 0.75 BA 2 0.185 31.35 4.70 0.81 BSF 3/16 0.1875 32 4.76 0.79 BSW 3/16 0.1875 24 4.76 1.06 MF 5 0.197 50.80 5 0.5 M 5 0.197 31.75 5 0.8 BA 1 0.2067 28.25 5.25 0.90 BSW 7/32 0.21875 24 5.56 1.06 BSF 7/32 0.2188 28 5.56 0.91 BA 0 0.2362 25.38 6.00 1.00 MF 6 0.236 33.87 6 0.75 M 6 0.236 25.40 6 1 UNEF 1/4 0.25 32 6.35 0.79 UNF 1/4 0.25 28 6.35 0.91 BSF 1/4 0.25 26 6.35 0.98 BSW 1/4 0.25 20 6.35 1.27 UNC 1/4 0.25 20 6.35 1.27

BA British Association BSF British Standard Fine BSW British Standard Whitworth M Metric Coarse MF Metric Fine UNC Unified Coarse UNEF Unified Extra Fine UNF Unified Fine

TPI Threads Per Inch

[nightjar]

The best way is a shadowgraph machine, but taking it to a shop is a lot cheaper if you don't already have a shadowgraph.

Colin Bignell

[Nick]

nightjar

What a good idea. As it happens, the department next door has something like that. A backlit or frontlit item can be magnified up to 100 times and displayed on a screen. This is what I need to tell the difference between Whitworth and Unified threads. If it works well I'll make my own shadowgraph just for that purpose.

[Guy King]

The message from Dave contains these words:

Funnily enough, last week. I was looking for M10 bolts and needed one with a cut thread 'cos I didn't want the shank undersized - and found some in B&Q. Which might explain why they were so sodding expensive.

[Dave Fawthrop]

|On Wed, 22 Mar 2006 19:17:43 +0000, Dave Fawthrop | wrote: | |>On Wed, 22 Mar 2006 19:08:42 GMT, Guy King wrote: |>

|>|The message |>|from Dave Fawthrop contains these words: |>| |>|> |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 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.

[Guy King]

The message from Dave Fawthrop contains these words:

Sadly they all are. They've gone the way of Halfords - bling and toys.

[dennis]

"nightjar .uk.com>"

A digital camera works quite well if it has a decent macro mode. I would expect a scanner to work too, you would need a reference like a ruler to measure the real sizes.

What's wrong with buying and trying a couple of nuts/bolts?

[nightjar]

I have to go out to buy bolts. The shadowgraph is in my workshop. I also have sets of thread form gauges, but haven't used them since getting the shadowgraph machine.

Colin Bignell

[Andy Luckman (AJL Electronics)]

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.

[Chris Bacon]

These selections are of very limited range.

Something "roughly right" won't do for many things.

[zymurgy]

That's because it's in B&Q, not cos of the manufacture.

Go to an engineering supplies, it'll also ensure the bolt is made of decent steel rather than camembert cheese.

HTH

Paul.

[Mathew Newton]

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

[Guy King]

The message from [e-mail] contains these words:

This was Sunday afternoon. Otherwise, I would indeed have gone to my local specialist as I have done several times before.

[Derek ^]

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

[Dave Plowman (News)]

You could scan it if you have a half decent scanner and compare to known thread profiles and sizes.

[Dave Plowman (News)]

If I scan something like a PCB on my ancient Epson GT-9500 and output it as a bitmap file to Draw on my even more ancient Acorn RPC I get an exact sized copy that (after treatment) can print out as a transparency to manufacture an exact reproduction. I dunno just how accurate it is in micron terms but would certainly be far more than adequate for things like mass produced thread measurements in the normal sizes.

[dennis]

Some of the newer CIS scanners aren't particularly good for 3D items.

[Dave Plowman (News)]

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.