Thread Size Guide

[poppypiesdad]

Hi all being relatively new to old vehicles and imperial nuts and bolts I came across this

 

http://www.thomassmithfasteners.com/thread_detective.html

 

Do you think it would be a worthwhile buy or just money down the tube

 

Jamie

[antarmike]

If it aslo covered BSF and BSW it might be worthwhile, but it seems an expensive extravagence... and if you have a damaged thread you whish to identify, the gauge will not enter the thread, so you are down to measuring diameter and pitch, with a vernier and rule, or pitch gauge if you are posh!

Edited February 6, 2010 by antarmike

[fv1609]

Jamie I think it would be more useful if it could distinguish between UNF, BSF, BSP that's where the difficulties come I find. Identifying UNF, UNC & Metric isn't usually too difficult & besides just trying a few known nuts isn't too much hassle particularly if it saves you £30 & besides with this kit you still have to try it on, so might as well use some from your own box.

Edited February 6, 2010 by fv1609

[antarmike]

A lot of info can be gained by spanner size that accurately fits the nut and bolt. And UNF UNC are visually easy to tell apart, and it is usually easy to identify UNF UNC by the fact the bolt head will have a circular recess in the head. UNF and UNC nuts will have a circular groove cut onto one of the closing faces, or have a series of interlocking circles stamped onto one or more spanner flats.

 

If the Bolt had a strength grade in raised figures on the head ( commonly 8.8) iit won't be BSW or BSF.

 

Strength grades are usually on Metric bolts.

 

You are highly unlikely to find BSP (Parallel or Taper) used on nuts or bolts. It is after all a standard for pipe threads, and will normally be on pipe fittings, blanking plugs and the like.

 

Also does not cover B.A. British Association threads you are likely to come across. And 0 B.A. is virtually identical in pitch and diameter to M6 course. Again refer to spanner size to differentiate.

 

I suggest you save your money and spend it on the actual nuts and bolts when you need them!

 

For most, but not all, small threads BSW and UNC threads share the same TPI (1/2" being the exception) , and if even slighly worn BSW will thread into UNC and Vice Versa. This is whether Spanner size is going to be the best clue. The only practical difference between most BSW and UNC threads is the flank angle (55 verses 60 degree) and I doublt whther these gauges will help there.

 

Whitworth BSF are fairly easy to recognise by sight because compared with UNF/ UNC and all the metric series the distance across the flats compared to the hread diamer is significantly larger. Ie if you look at the ratio of across the flats head size compared to thread size. BSW and Whit are significantly larger than UNF and UNC and Metric.

 

I would seriously suggest learning the visual clues as to threads before spending this money. Parts book may tell you anyway, as might the manual which might say "engine threads are unified" meaning UNC/ UNF. Or in some military situations the thread standard is stencilled onto the engine.

 

Where I say refer to spanner size, the same applies to hex sockets screw, hex grub screws. Metric use Metric allen Keys, BSW/BSF UNC and UNF all use Imperial A/F Allen. B.A. Grub screw also use Imperial allen keys, allthough there are unique Spanner sizes for B.A. nuts and Bolts.

Edited February 6, 2010 by antarmike

[antarmike]

I hope this may be of use. Can E-mail to any-one who has difficulty knowing what spanner fits which bolt, or which thread it is likely to be by measuring across the spanner flats. Also useful for finding next biggest or next smallest spanner...

Edited February 6, 2010 by antarmike

[antarmike]

If the bolt head or nut is metric across flats size, here sre the standard thread diameter for Metric Spanner flats to ISO standards

Spanner size- thread size

7- M4

8- M5

10- M6

11- M7

13- M8

14- M9

17- M10

19- M12

22- M14

24- M16

27- M18

30- M20

32- M24

Edited February 6, 2010 by antarmike

[FWDTEXAS]

A usefull tool for restores that do multiple items.

[Adrian Barrell]

And remember, before the war, BSW head sizes were bigger than their equivelant BSF sizes which is why a spanner is sometimes marked 3/8 BSW-7/16 BSF. This explains why a modern 3/8 dia BSW bolt needs a 5/16 BSW spanner.

[antarmike]

And remember, before the war, BSW head sizes were bigger than their equivelant BSF sizes which is why a spanner is sometimes marked 3/8 BSW-7/16 BSF. This explains why a modern 3/8 dia BSW bolt needs a 5/16 BSW spanner.

 

Yes forgot to say that in the charts above where it says under British sizes" BS that means both BSF and BSW the post war standard, where it refers to W that is the prewar Whitworth standard.

[ruxy]

If only life was so easy !

 

It is in fact a good tool to have , probably if requested the makers would run a batch off for BSF , BSW , BSP etc.

The alternative is to have a good supply of taps & die-nuts as a double check.

Put two supposed same M&W thread pitch guages together and there is often a error, Starrett are much better in that respect.

 

In the real world on cars - you will in fact find you are using your 9mm 11mm 12mm 14mm 15mm 16mm & 18mm more often than you would expect , often 16mm & 18mm are found on fuel injection fittings. 11mm 12mm 14mm and 15mm because cars tend to use flange bolts and hex. nuts requiring a smaller smanner size than nominal for the fixing thread dia. - so spanners are not a good guide. You often get cylinder head stretch bolts having a dia. of 9mm , they don't all have a Torx head - often they are a hex. flange head. A few years ago I was foxed when I came across a 7mm bolt.

Then of course - on older metric cars - the so common 8mm dia thread standard bolt - in fact used the 14mm hex. spanner (that was slimmed down to the now accepted 13mm).

Even to this date - you will find metric hex. head sizes against nominal bolt head (plain sets & shoulder bolts) can vary depending on three common metric standards German DIN , NFE - Nationalistic France has its own National Euro standard and Sweden with its SMS Swedish metric standard.

[antarmike]

If only life was so easy !

 

It is in fact a good tool to have , probably if requested the makers would run a batch off for BSF , BSW , BSP etc.

The alternative is to have a good supply of taps & die-nuts as a double check.

Put two supposed same M&W thread pitch guages together and there is often a error, Starrett are much better in that respect.

 

In the real world on cars - you will in fact find you are using your 9mm 11mm 12mm 14mm 15mm 16mm & 18mm more often than you would expect , often 16mm & 18mm are found on fuel injection fittings. 11mm 12mm 14mm and 15mm because cars tend to use flange bolts and hex. nuts requiring a smaller smanner size than nominal for the fixing thread dia. - so spanners are not a good guide. You often get cylinder head stretch bolts having a dia. of 9mm , they don't all have a Torx head - often they are a hex. flange head. A few years ago I was foxed when I came across a 7mm bolt.

Then of course - on older metric cars - the so common 8mm dia thread standard bolt - in fact used the 14mm hex. spanner (that was slimmed down to the now accepted 13mm).

Even to this date - you will find metric hex. head sizes against nominal bolt head (plain sets & shoulder bolts) can vary depending on three common metric standards German DIN , NFE - Nationalistic France has its own National Euro standard and Sweden with its SMS Swedish metric standard.

 

 

And in the early days of metrication manufacturers where using up 3/4" hex bar stock, stamped with the Unified interlocking circle mark, to turn 19MM spanner flat M12 nuts and bolts out of! With only 2 thou diierence in size I guess they thought what the heck..

Edited February 6, 2010 by antarmike

[croc]

If only life was so easy !

 

In the real world on cars - you will in fact find you are using your 9mm 11mm 12mm 14mm 15mm 16mm & 18mm more often than you would expect

 

I have hardly got any metric stuff - it's the devils work...

[antarmike]

If only life was so easy !

 

It is in fact a good tool to have , probably if requested the makers would run a batch off for BSF , BSW , BSP etc.

The alternative is to have a good supply of taps & die-nuts as a double check.

Put two supposed same M&W thread pitch guages together and there is often a error, Starrett are much better in that respect.

 

In the real world on cars - you will in fact find you are using your 9mm 11mm 12mm 14mm 15mm 16mm & 18mm more often than you would expect , often 16mm & 18mm are found on fuel injection fittings. 11mm 12mm 14mm and 15mm because cars tend to use flange bolts and hex. nuts requiring a smaller smanner size than nominal for the fixing thread dia. - so spanners are not a good guide. You often get cylinder head stretch bolts having a dia. of 9mm , they don't all have a Torx head - often they are a hex. flange head. A few years ago I was foxed when I came across a 7mm bolt.

Then of course - on older metric cars - the so common 8mm dia thread standard bolt - in fact used the 14mm hex. spanner (that was slimmed down to the now accepted 13mm).

Even to this date - you will find metric hex. head sizes against nominal bolt head (plain sets & shoulder bolts) can vary depending on three common metric standards German DIN , NFE - Nationalistic France has its own National Euro standard and Sweden with its SMS Swedish metric standard.

 

This post atred with the words "I am relatively new to the world of OLD VEHICLES",

If I had known we were talking Modern vehicles I would have included the use of pentagon heads as well as hexagon heads, but I thought we were talking about older military vehicles that were built with BSF/BSW UNF/UNC where tapped holes in castings etc will retain the threads they were built with, but maybe brackets, bodywork fixings and similar through hole fixings between two parts have been replaced with standard ISO nut and bolt of near match size, obtained from a nut and bolt stockist. In which case the Metric spanner flat to thread size data I provide is absolutely correct. I like Croc have not yet encountered Metric threads used from new on any old military vehicle I have worked on.

Edited February 6, 2010 by antarmike

[Richard Farrant]

I like Croc have not yet encountered Metric threads used from new on any old military vehicle I have worked on.

 

Morris Commercial trucks prewar and WW2 era had some metric threads in them, chiefly in gearboxes and possibly engines, the rest was BSF / BSW. Reason being that Morris bought the Hotchkiss business in Coventry in mid war period, and they built components for the trucks, their background being arms manufacturing with roots in France, hence they were using metric tooling.