Thread gauge question

[Jeff2]

Hi All--

I did a search for my question, but didn't find anything specific on it. But let me know if there's a thread already up someplace that answers it.

I am restoring a 1971 Triumph motorcycle, and I know about the different thread types that I might find on the bike. My question is, what thread gauge should I buy, and how do thread gauges work? Normally if I take something apart I bag it, tag it, etc so I can put it all back together correctly. But this bike came as a pile of parts, so I'm going to need to figure out which fastener goes where by using the parts / shop manuals and measuring.

Thanks,

Jeff

[BTF]

Our gauges are standard Whitworth leaf gauges see: http://www.britishfasteners.com/mm5/merchant.mvc?Screen=PROD&Store_Code=BTF&Product_Code=7595&Category_Code=

They contain Whitworth thread form leafs with 55 degree angled threads on them in sizes from 1/16" to 2" (ranging 60 TPI to 4-1/2" TPI)

Although BSCycle and CEI (cycle engineers institute) threads have 60 degree angled threads, you can still use them to determine the number of threads per inch.

Simply place a leaf on the screw/nut in question until you can determine the best fit. I find that holding the gauge and screw up to the light to see if any shines through the gaps works well to determine the best fit.

If you have a bag of hardware and are looking for replacements, you will need to determine two things.
1) The O.D. of the thread (1/4", 5/16" etc)
2) The number of threads in one inch. This is where the thread gauge works.

You will also find that these Tapping Drill Charts are useful too:
http://www.britishfasteners.com/images/nuts_bolts_key.pdf
http://www.britishfasteners.com/threads/index.html
http://www.britishfasteners.com/fractions.pdf

[Jeff2]

Thanks for the info and the charts. For my U.S. edition Iriumph, I've been told there may be SAE fasteners (UNF, UNC), as well as BCF, BSW, BSC, CEI, and maybe even a metric here and there. Is there a way to differentiate these beforehand, or is trial and error the only way? I have a Parts Manual with a table of standard hardware, which only lists UNF and UNC. This would be good news if it were true of all the fasteners. I'm not doing the engine myself--having it professionally rebuilt, so maybe this won't turn out to be such a difficult problem.

Meanwhile, I will order your thread gauge.

Thanks again!

Jeff

[BTF]

Thanks for the info and the charts. For my U.S. edition Iriumph, I've been told there may be SAE fasteners (UNF, UNC), as well as BCF, BSW, BSC, CEI, and maybe even a metric here and there. Is there a way to differentiate these beforehand, or is trial and error the only way? I have a Parts Manual with a table of standard hardware, which only lists UNF and UNC. This would be good news if it were true of all the fasteners. I'm not doing the engine myself--having it professionally rebuilt, so maybe this won't turn out to be such a difficult problem.

Meanwhile, I will order your thread gauge.

Thanks again!

Jeff

If you are having it professionally rebuilt you may not have to worry as much but it would still be a good idea to familiarize yourself with the hardware in case you have to do some minor repairs yourself one day.

Without measuring the thread OD and counting the TPI, you could tell a BSW/BSF/BSC bolt or nut by the difference in the hex head. Re-review the Key to nut and bolt sizes that I linked before. You can see the hex sizes for British hardware on it.

I should point out though, that some of the differences between US and British are so minor that you may not be able to be 100% sure. Besides this, measuring the head size AF will only tell you if the bolt is British, it wont tell you whether it is a BSW, BSF or BSC

You follow? lol

[Jeff2]

Many thanks! I'm starting to get it :)

[BTF]

Many thanks! I'm starting to get it :)

Yes, it can be a bit confusing. If you need any help, just ask. :)