# Imperial bolt/stud sizing - this has me confused...



## FlowolF (18 Nov 2015)

I have a rolling mill for non-ferrous metals and need to replace the bolts that hold the top plate down - the originals were uhhmmm 'rubbish', far shorter than the threaded holes were deep, and they stripped during a job - these are imperial UNC threaded bolts, but the outside diameter of the threads of the actual bolts is 7.7mm, and I can't for the life of me find a match - ~6.25mm would be 1/4 inch if I have it right, but next size up is 3/8 and that's around 9mm I think - can any of the wise folk here enlighten me before I knock this wall down with my head?

Cheers!

',;~}~

Shaun/FloWolF

Oh, it's bloomin' 5/16 isn't it (smacks forehead!) - Can't believe I've missed that for days - where's the delete post button?!? :-/


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## CHJ (18 Nov 2015)

http://www.quest42.co.uk/woodwork/html/ ... ersion.htm


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## Wildman (18 Nov 2015)

5/16 it is, hee hee


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## FlowolF (18 Nov 2015)

Thanks Chas - miles more helpful than _any_ of the charts I managed to find - now bookmarked!

Wildman - please laugh all you want, that way at least *something* useful has come out of my total and utter 'bairn frat', because the _3/8_ inch UNC high tensile threaded bar I got via e-bay will likely not be, at all, ever lol!

Cheers!

Shaun/FloWolF ',;~}~


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## bugbear (18 Nov 2015)

FlowolF":22t03o2i said:


> I have a rolling mill for non-ferrous metals and need to replace the bolts that hold the top plate down - the originals were uhhmmm 'rubbish', far shorter than the threaded holes were deep, and they stripped during a job - these are imperial UNC threaded bolts, but the outside diameter of the threads of the actual bolts is 7.7mm, and I can't for the life of me find a match - ~6.25mm would be 1/4 inch if I have it right, but next size up is 3/8 and that's around 9mm I think - can any of the wise folk here enlighten me before I knock this wall down with my head?
> 
> Cheers!
> 
> ...



As bacakground;

Did you try measuring the pitch of the (surviving) thread?

Often more informative than the OD, which can vary, even for a given nominal size.

BugBear


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## Wildman (18 Nov 2015)

FlowolF":3jw53ef0 said:


> Thanks Chas - miles more helpful than _any_ of the charts I managed to find - now bookmarked!
> 
> Wildman - please laugh all you want, that way at least *something* useful has come out of my total and utter 'bairn frat', because the _3/8_ inch UNC high tensile threaded bar I got via e-bay will likely not be, at all, ever lol!
> 
> ...


Sorry to laugh, I cannot help thinking in imperial and forget that it is alien to many younger people, just as measuring and visulising in metric is alien to me. It was intended in good heart believe me.
If measuring an imperial item you will find it easier to use imperial units from the start then you don't get lost in the conversions. Do remember to tap out the holes before trying to screw new bolts in, or drill and tap out to the aforsaid 3/8 UNC for better holding power. (at least three threads deep mind).


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## FlowolF (18 Nov 2015)

bugbear":sb5x4sxw said:


> FlowolF":sb5x4sxw said:
> 
> 
> > I have a rolling mill for non-ferrous metals and need to replace the bolts that hold the top plate down - the originals were uhhmmm 'rubbish', far shorter than the threaded holes were deep, and they stripped during a job - these are imperial UNC threaded bolts, but the outside diameter of the threads of the actual bolts is 7.7mm, and I can't for the life of me find a match - ~6.25mm would be 1/4 inch if I have it right, but next size up is 3/8 and that's around 9mm I think - can any of the wise folk here enlighten me before I knock this wall down with my head?
> ...



Aye bud - it's a standard UNC thread.

Cheers!

Shaun.


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## FlowolF (18 Nov 2015)

Wildman":2u5rgcse said:


> FlowolF":2u5rgcse said:
> 
> 
> > Thanks Chas - miles more helpful than _any_ of the charts I managed to find - now bookmarked!
> ...




Heheh, don't EVER be sorry for laughing, certainly not on my account mate! I was laughing heartily at myself, and my 'plea' for you to laugh all you wanted was sincere ',;~}~

As for the rest, well yeah at a whisker short of 47 y/o I'm perhaps a little young for imperial fluency.

And believe me I would have measured it in imperial, but the best my tools can do is in base 10 divisions of imperial units, and I wouldn't have the foggiest where to take 10ths of an inch into 8ths or 16ths, or having dealt with BSP measurements a few times, even what the darned sizes actually refer to, in factual actual reality lol.

No imperial taps in my kit, but luckily only the top few threads are damaged at all, since the bolts only extended that far down, despite the holes being over 1/2 inch deep with most of that being threaded, and also the original bolts were under diameter as well (I'd found some better bolts already they just still weren't long enough - it was these found bolts I got the 7.7mm diameter from) - what can I say, it was a low cost roller mill, made in India to an old English design, as so many of these sorts of things are and I suppose at the price I paid, something had to give.

I'm going to replace them with high tensile studs slotted for a screw driver, then they are getting driven fully home (3 threads wouldn't hold the forces on this for very long even with new bolts), before being secured with high tensile steel nuts - this part of the mill at least, shouldn't fail again - cheers Wildman, and g'night fella!

',;~}~

Shaun.


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