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Anonymous Poster

How to Use a Thread Plug Gauge

10/06/2010 5:13 PM

Hi All, Recently I had some machined internal threads knocked back. I'm sure there is a standard for how many turns a nogo can enter the thread. I've found the american standard, a jis standard and an ISO standard. Is there a BS standard? Does anyone know what it is, and where I could possibly see it? We ended up cutting/welding and remachining the part because the QC wouldn't ring the customer and ask what was acceptable and just steadfastly believed nogo means no.

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#1

Re: How to Use a Thread Plug Gauge

10/06/2010 6:52 PM

I've no doubt there is a BS that covers this - I don't know what it is, but I'm 99% sure you'll have to pay to get a copy of it. You may be able to request it at a public library - you can do this in the UK (but you can't make copies). Don't know if there is any arrangement with libraries elsewhere in the world. Sorry.

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#2

Re: How to Use a Thread Plug Gauge

10/06/2010 8:14 PM

Contact the manufacturer of the thread gauge. They will know the correct operating procedures for the gauge.

For internal threads, the go gauge tells if the threads are too small. The no go gauge tells if the threads are too large. If it's a straight thread, the no go gauge would go all the way, showing an oversize thread.

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#3

Re: How to Use a Thread Plug Gauge

10/08/2010 1:09 AM

Dear Guest, The regular practice is NoGo is permitted to enter max of one full thread. Regards Ragavan

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#4

Re: How to Use a Thread Plug Gauge

10/08/2010 2:15 AM

I would use the ISO standard - they are gradually replacing the BS, and many are just updates of the current BS.

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#5

Re: How to Use a Thread Plug Gauge

10/08/2010 2:26 AM

Try googling it, as obviously there is a BS standard - the B meaning British and the S - Standard !

Be sure when checking the BS standard - it could be BSF - British Standard Fine, or even BSW - British Standard Whitworth

JIS is no good as it is Japan Industry Standard.

ISO isn't universal yet. It a METRIC based system.

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#6

Re: How to Use a Thread Plug Gauge

10/08/2010 4:20 AM

Yes their are go/no go gauges available for BS threads, gauges can normally be purchased for the likes of BSPP or BSPT, these are pretty self explanary when you use them.

One of the problems that I have had in the past is when the likes of Couplings have been welded into something that causes localised shrinkage, the only thing to do is re tap the Coupling very carefully otherwise it makes the gauge too sloopy in the thread.

Best of luck

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#7

Re: How to Use a Thread Plug Gauge

10/08/2010 4:55 AM

You need a copy of Screw Thread Manual by E.J.Camm. 1942

You first need to establish what type of BS thread you are cutting.. BSW (whitworth) BSF (fine) BA.. BSP (pipe)or BSC (cycle) and what size. If you have a drawing I could help you or send you a pic of the pages from the book..

Hope this helps you..

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#8

Re: How to Use a Thread Plug Gauge

10/11/2010 3:49 PM

The standard Your after is BS919 Screw Gauge Limits and Tolerances, which comes in 4 parts.

BS919-1 --Unified Thread Forms

BS919-2 --Whitworth and BA Thread Forms

BS919-3 --Isometric Thread Forms

BS919-4 --Unified Thread Form 1/4" and above

It states -section A.1.2 :"Ideally it should not be possible for the guage to enter the product thread but, as internal threads are often slightly bellmouthed, it is permissable to allow entry provided that, on withdrawal, disengagement takes place withing two full turns of the thread. If the product has a length of thread of three turns or less, the guage should not screw completely through the product thread. The guage should be applied by hand without using excessive force."

You can buy a copy from BSI online, or as mentioned maybe even see a copy at a library.

I normally have 1 to 1.5 turns as my maximum, depending on thread, and thread depth.

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#9
In reply to #8

Re: How to Use a Thread Plug Gauge

10/11/2010 7:02 PM

Hi bones,

Well said, and welcome to CR4.

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#10

Re: How to Use a Thread Plug Gauge

03/23/2011 3:47 PM

The regular practice is NoGo is permitted to enter max of one full thread

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