Imperial bolt ID

[hotponyshoes]

Anybody know what thread these are?


Fitted to some fairly modern American kit

O/d of thread measures 4.1mm
Can't find my pitch gauge, seems to be about 7 threads per 6mm.
So roughly 1.16mm pitch which may or may not be about 21/22 tpi?

A 3/32 hex key fits pretty nicely

 

[The_Yellow_Ardvark]

1/4 UNC I would guess at.

 

[Kram]

Retap the kit M5

 

[RWD3M]

Anybody know what thread these are?
View attachment 249940

Fitted to some fairly modern American kit

O/d of thread measures 4.1mm
Can't find my pitch gauge, seems to be about 7 threads per 6mm.
So roughly 1.16mm pitch which may or may not be about 21/22 tpi?

A 3/32 hex key fits pretty nicely

Hi Ponyshoes,

First off, I think your maths may be a little suspect.

If you have 7 threads per 6mm, then you have 14 per 12mm and therefore 28 threads per 24mm, so around 30 threads per 25.4mm (inch) or a pitch of about 0.85mm.

4.1mm is, give or take, 5/32" and both 5/32" (or No.8) UNC and 5/32" BSW have 32 TPI, so not too far out.

Does it screw into ally by any chance?

 

[hotponyshoes]

Hi Ponyshoes,

First off, I think your maths may be a little suspect.

If you have 7 threads per 6mm, then you have 14 per 12mm and therefore 28 threads per 24mm, so around 30 threads per 25.4mm (inch) or a pitch of about 0.85mm.

4.1mm is, give or take, 5/32" and both 5/32" (or No.8) UNC and 5/32" BSW have 32 TPI, so not too far out.

Does it screw into ally by any chance?

My maths is fine, 7÷6 is 1.16.
My common sense is not so good as it should be 6÷7 to get the correct answer of 0.85mm pitch!

It does indeed screw into alloy, how do I work out if its unc or bsw? Its American so unc?

 

[RWD3M]

My maths is fine, 7÷6 is 1.16.
My common sense is not so good as it should be 6÷7 to get the correct answer of 0.85mm pitch!

My maths is fine, 7÷6 is 1.16.
My common sense is not so good as it should be 6÷7 to get the correct answer of 0.85mm pitch!

It does indeed screw into alloy, how do I work out if its unc or bsw? Its American so unc?

Almost certainly UNC. I don't think the Americans would know a Whitworth thread if it jumped up and bit them on the proverbial!

They are out there, e.g. https://www.accu.co.uk/en/imperial-socket-countersunk-screws/30518-SSK-8-32-3-8-A2 or http://www.modelfixings.co.uk/Stainless_unc_countersunks.htm

The only practical difference is the thread angle. 60 deg on a Unified (UNF, UNC etc) thread and 55 deg on anything devised by Sir Joseph!

 

[The_Yellow_Ardvark]

@hotponyshoes

I may have some black ones if you want and they are UNC.

 

[hotponyshoes]

1/4 UNC I would guess at.

1/4 would be 6.something o/d wouldn't it?

I need 6 of these but at 1.5" long. Black would be fine if you happen to have any?

 

[The_Yellow_Ardvark]

Will look in the next 24 hours.
Doc says no play pen.

 

[8ob]

UNC and Whit use different countersink angles. Whit are 100 and UNC 82.5

Bob

 

[Hopefuldave]

UNC and Whit use different countersink angles. Whit are 100 and UNC 82.5

Bob

Thread flanks are different too, UN are 60* like metric (and have flats top & bottom like metric), BSW / BSF are 55* and have radii, that's why they're stronger...

Dave H. (the other one)

And don't get me started on BA...

 

[RWD3M]

Thread flanks are different too, UN are 60* like metric (and have flats top & bottom like metric), BSW / BSF are 55* and have radii, that's why they're stronger...

Dave H. (the other one)

And don't get me started on BA...

Ah, BA, based on the metric system!

 

[Maker]

And don't get me started on BA...

Just googled that, I had no idea they were so confusing!

 

[Hopefuldave]

Just googled that, I had no idea they were so confusing!

It's the calculating diameters and pitches using logarithms... Get out the book... https://www.ebay.co.uk/itm/223996878926

Dave H. (the other one)

 

[Maker]

No thanks, I'll stick to nice easy UN and whit threads, my lathe only pretends it can do metric threads anyway and certainly not multiples of 0.9mm

 

[grim_d]

Thread flanks are different too, UN are 60* like metric (and have flats top & bottom like metric), BSW / BSF are 55* and have radii, that's why they're stronger...

Dave H. (the other one)

And don't get me started on BA...

Don't tar all with one brush, UNJ threads have a radius.

 

[Agroshield]

8-32 x 1 1/2" UNC stainless countersunk

https://www.ebay.co.uk/itm/4-40-6-3...Machine-Screw-A2-Stainless-Steel/263893172232

 

[hotponyshoes]

I'm more confused now!
Is 8-32 the same as 5/32?

Ie a #8 bolt at 32 tpi?

 

[Agroshield]

I'm more confused now!

[YANK]But imperial is so much better and simpler than metric[/YANK]

From here:

https://en.wikipedia.org/wiki/Unified_Thread_Standard

Diameter of numbered thread = (number of thread x 0.013) + 0.060

So number 5 is 1/8" dia.

If I may, could I suggest an imperial ruler for pitch measurement. Count the threads over 1/2" of length. If the old earsight is not so hot, a good close-up photo sent from phone to widescreen monitor helps a lot.

 

[MattF]

No thanks, I'll stick to nice easy UN and whit threads, my lathe only pretends it can do metric threads anyway and certainly not multiples of 0.9mm

That's why man invented taps & dies.