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Evening guys,looking for a gunsmith in newport/bristol area to do some work on my tikka as I'm having issues with the screws for the rail that screw into the action.

Think I might have damaged the threads trying to get them in.

Atb dave 

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Presumably you mean the scope rail? The action is hardened AFAIK, so it's more likely that the screws are mashed.

Had this with my M595.............thinking that as it's made in Finland, it would have metric threads instead of the yank abortions, I tried using M3.5 screws. The first one jammed and stripped, so I realised I had the wrong size...........the M595 action is threaded 6/48, whatever that means.

Sorted it, though, just managed to winkle the spiral of stripped metal out of the hole, and got some 6/48 screws from Brownells.

Pete

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It means it’s a No6 wire gauge size (actually British) and 48 TPI

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Well I looked up the diameter of no. 6 SWG , and according to   https://www.rapidtables.com/calc/wire/swg-to-mm.html   it's 4.877mm, whereas the 6-48 screws that I have (which fit)  are 3.38mm in diameter..................

Pete

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50 minutes ago, 20series said:

HPS-TR are up the M5 At Newent.

Alan

Thanks,just dropped them an email.

Atb dave 

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It is almost certainly a custom thread, based on UNF #6.

UNF #6 is normally 40 tpi, but it is a custom at 48 tpi.

OD should be 0.138", which converts to 3.505 mm 

60 degree flank angle.

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6-48 NS is most likely a Unified thread commonly used rifles especially American built.

NC is Course, NF is Fine, NEF is extra fine, the NS stands for Special thread.

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Matt

Interestingly (and not looking for an argument on this, it is purely a nerd comment), as you say UNS, the Unified Specials, are basically anything that aren't NC, NF or NEF.

However, and peculiarly, you won't find #6 - 48 on any list of UNS threads as they only start at #10-28.

So, #6-48 is really a custom thread based on UN #6 diameter and thread form, rather than an actual UNS thread.  It's a special, but it isn't UNS, it's a custom.

The only reason I mention it is because if people go looking for a definition of 6#-48 UNS, they likely won't find it on any of the UNS thread charts .

Machinery's Handbook is probably the definitive bible, and #6-48 doesn't appear on the UNS charts in my copy.

Hope that makes sense 😂

 

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Pretty sure uns is for big stuff where the tpi is fixed at 8,  when above 1 inch regardless of diameter.

Chris

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Dave,

I have a set of 6-48 taps and dies here that have NS on them. I would have thought with things called 'special' there would be plenty of variation around.

This is part of a chart I have from a supplier in the States (Lincoln Machine Tool IIRC).

Quote
To Tap This Size Screw Or Bolt: Use This Drill Bit: (Closest Fractional:)
6-32 NC #35 7/64"
6-36 NS #34 -
6-40 NF #33 -
6-48 NS #31 -

 

There's also a Chart from Hanson LINK

The Hanson chart goes from #4NS to 1/4"NS. Most charts I have found (Such as this one) start at #10 and go from there but apparently they go smaller and possibly bigger.

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I believe that 6x48 could also refer to 6BA (British Association Standard Thread).

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3 hours ago, MarkR said:

I believe that 6x48 could also refer to 6BA (British Association Standard Thread).

Mark

In a word, no.

UN (Unified) threads are American, with a 60 degree flank angle, imperial measurements.  

We have already established that the #6-48 referred to is 0.138" diameter (3.505 mm), 48 tpi.

Despite the misnomer, the British Association thread form is actually of Swiss origin, and is a metric thread form.

6BA is 0.110 diameter (2.8 mm), pitch is 0.53 mm, flank angle is 47.5 degrees.

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40 minutes ago, David TS said:

Mark

In a word, no.

UN (Unified) threads are American, with a 60 degree flank angle, imperial measurements.  

We have already established that the #6-48 referred to is 0.138" diameter (3.505 mm), 48 tpi.

Despite the misnomer, the British Association thread form is actually of Swiss origin, and is a metric thread form.

6BA is 0.110 diameter (2.8 mm), pitch is 0.53 mm, flank angle is 47.5 degrees.

David, thank you for your precise reply, I  didn't see any diameter being referred to and was only putting forward 6BA as a possible suggestion as the number of threads work out at 47.92 TPI.  I was given the 19th Edition of the  Machinery's Handbook upon finishing my Engineering Apprenticeship many moons ago, and I couldn't find any reference to 6-48 within it.   Regards MarkR

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Mark

I noticed that the conversion of 6 BA to imperial was 47.92 tpi, and suspected that was what made you think of it.

Your edition of Machinery's Handbook is newer than mine, mine is the 14th, but lots of the data probably hasn't changed since the 1st edition in 1914! 😄

My engineering apprenticeship started at Marconi in 1969.....😮

Regards

David

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15 hours ago, David TS said:

Mark

I noticed that the conversion of 6 BA to imperial was 47.92 tpi, and suspected that was what made you think of it.

Your edition of Machinery's Handbook is newer than mine, mine is the 14th, but lots of the data probably hasn't changed since the 1st edition in 1914! 😄

My engineering apprenticeship started at Marconi in 1969.....😮

Regards

David

David, the 19th Edition was published in 1974 - it says that there was a Total Issue of 1,919,000 at that time (since 1914).  I think 6-48 must have been so obscure it was dropped from our editions... 😉

My apprenticeship started in August 1971 and finished in August 1975.  Most of the time it was hands-on using various machines  (lathes, grinding, jig boring, etc.) ending up in the Planning & Estimating department where I remained for 18 months until I was promoted to Staff and became the Companies Chief Engineering Inspector.... that is when I learnt the art of diplomacy.... once an apprentice, always an apprentice.  Left engineering in 1987 to manage other people's money....

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