Bolt/Set screw sizes 101

[Discotroll]

Hello knowledgeable Austin 7 owners -

I have a question of a very basic nature - my Austin 7 came in a series of cardboard boxes and on the list of missing things were the bolts/set screws that hold the two halves of the differential case together along with with bolts/set screws that hold the torque tube to the differential housing. Could anyone advise me of the size/length I need for these two jobs (standard 1934 D type diff. Housing) - all help would be really appreciated...

[David Cochrane]

I think that the axle casing is held together by six 5/16" BSF x 3/4” bolts (plus lockwashers).

[Discotroll]

Excellent - thank you for the info!

[Chris KC]

Nearly all fixings on an A7 are BSW or BSF. It's worth seeking out a copy of the relevant thread tables (diameter, pitch, tapping hole size, etc) and sticking them on your garage wall then you'll be able to identify them with relative ease. You will of course come across BA threads, metric interlopers and 'unified' monstrosities introduced to your car by former owners. Plus there are one or two 'special' threads to watch out for, but all in good time.

[Howard Wright]

Hi

This excellent web page from the Cornish A7 club is my go to reference for thread sizes.

https://www.austin7.org/Data%20Pages/Tech%20Data/

Cheers

Howard

[Discotroll]

Thanks Howard - that is exactly what I'd originally hoped to find but came up short - as suggested a copy of that on the garage wall will be invaluable...

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'Special threads' - you've gotta love the British car industry! 

[dickie65]

Sump Plug is an Admirality Thread.
The Thread form is Whitworth but the diameters are Bastard.
Admiraity threads used the same TPI for several different diameters
The sump plug and back axle plugs are 3/4" with a 14 TPI whitworth thread.
14 TPI was used on about 5 different diameters which do not match any standard Whitworth Threads
I had to go back to 1940s engineering Data books to find the information.
I now have the correct Taper tap for these 3/4" 14 tpi threads which I found on ebay for beer money.
I did the research as I am repairing a 9E Nippy Sump which had the thread stripped out.

[Steve kay]

There are probably numbers of us whose stores and workshop shelves are packed with jam and mayonnaise jars full of fastenings. Whitworth allegedly the usual older threads, but Zenith and Solex capable of metric use. Then we come to BSF and BA. Any older Ford engines, even thuogh built in Cork or Dagenham, bring  UNF and some UNC. Previous owners upon whose heads curses maybe pronounced, may have used metric. As discussed above, the TPI is not restricted to any thread profile. Workshops shared with senior bicycles quadruple the number of threads, some builders such as Raleigh and early Sunbeam had threads of their own. Oh the hours of fun raking about for fastenings! Some specialists have been researching the great big threads used in cider presses in the Marches. Well done them, we look forward to their books in due course.

[Colin Wilks]

To add to the collective knowledge, the grub screws that hold the wires into the dynamo terminals (and on the back of many dash board gauges) are 1/4" BSF (26 tpi) - no prizes for guessing why I needed to know this.