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Nut & Bolt Sizes.

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John Flack17/03/2017 10:17:23
164 forum posts

Howard L gives solid advice in his post avoiding nugatory tarradiddle BUT as fasteners can be brass, steel, high tensile, half nuts aero nuts etc etc this raises the question should an amateur even consider reusing any fastener of unknown origin? The experienced can make an informed choice, much will depend on the use to which it is to be put.

As an amateur who has rebuilt motor vehicle engines, certain fasteners that I would classify as "stressed" would be replaced with known quality replacements. I would never re use a nylon/aero type nut. Just my personal logic with no science to back it up. The old items being junked to avoid mishaps.

Nigel McBurney 117/03/2017 11:08:45
503 forum posts
3 photos

I was asked to make a fuel jet for a old David Brown tractor carburettor ,probably a petrol paraffin tractor.knowing that some carbs had French origins,I careful checked the old jet,and the carb body as to was die cast and any error on my part may damage the thread in the old and frail die casting,it was as I suspected French metric not ISO the difference is .05 of a mm in pitch on a m4 thread,not much but enough to wreck the die cast thread.the customer was more than happy with jet and a couple spares,he had to bear the cost of a new tap and die but did not care and told me to keep them. I had learnt about 50 years ago that metric pitches can vary, from an engineer i worked under at the time so I went and bought a machinery's screw thread handbook which has proved to be so useful.

John Flack17/03/2017 17:34:04
164 forum posts

Ah French fine thread. Important if you own a MG TD TF 1500. As Michael Caine said " not........................................!

vintagengineer18/03/2017 00:17:07
408 forum posts
6 photos

Bugatti uesd all odd number metric threads and Austin used Admiralty Fine threads right up to the very last Mini Metros!

Richard S220/03/2017 21:32:49
124 forum posts
67 photos
Posted by John Flack on 13/03/2017 10:27:48:

Chart sizes indicate that 20BA nuts are possible. Has any living soul ever seen a nut of this size, and where can I get some?

Smallest A/F steel Nuts/Bolts for me so far are the ones I made. 0.0669" (1.69mm) A/F from my Commercial Hex Steel Rod stock, shown here in the middle-


The other 12BA (lower) items are commercially made.

The top 14BA items are also commercially made.

I could only find 16BA (brass) nuts listed in my 30 year old price list from Clerkenwell Screws Ltd .Smallest Steel was 14BA.

My reference book extracts state that BA sizes from #17- 25 are generally unavailable, having been replaced by Watch, or Horological thread forms (not sure when).


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