Banjo bolt sizing

[lawnmowerman]

OK hands up, it's not from a BSA but I am hoping someone can help identify the size of this banjo bolt so I can order some.

It is from a 1938 Wolseley and they are used on the Lockheed brake wheel cylinders. They probably had not been taken out for 74 years and I butchered the heads on two of them.
 
Thanks

[bonny]

7/16" sae (society of automobile engineers) standard (sae std) ? This is 20 tpi for 7/16".

[lawnmowerman]

Thanks Bonny. I spent about an hour on the net looking up thread size charts and gave up and had a beer!

Jim

[bonny]

Handy chart here.    http://mdmetric.com/tech/tic1d.htm

Or engineers toolbox website is invaluable too.

http://www.engineeringtoolbox.com/

[Beezageezauk]

Jim

7/16 X 20tpi could be one of a couple of threadforms.  Favourites would be cycle thread (CEI) or UNF.  Both are very similar but I don't know if they are interchangeable.  I would guess, if it's from an old British car, that it would be cycle thread.  UNF, at that time was predominantly used on the American market.  Note that 7/16 cycle thread is also available with 26TPI.

Ok, on stating the above, I'm no expert with thread forms and others on this forum will probably have much more knowlege than me on the subject.

I know that the British cars from the 1970's and 80's used a 7/16 x 20 thread on their seat belt anchorages but the bolts were threaded all the way down so couldn't be modified to suit your purpose.  You could maybe check the thread if you have one kicking about.  I have a couple here.  If you want to try one send me a PM with your address and I'll put one in the post for you.

At least it would be a start.

Beezageezauk.

[bonny]

It shouldn't actually matter what thread form it is , you have the major diameter and the pitch , so anyone with a lathe should be able to turn you up a couple. But it think beezageezer is correct  , sae and unf became the same after the war or sometime around then.

The old book of threads (1919) i have doesn't list any details between 3/8" and 9/16" for cycle , suggesting there is a duplicate in some other form , eg. Sae or unf, no 7/16" cycle listed, but 9/16" has 20 tpi so its a good bet 7/16" is 20 threads too.

[lawnmowerman]

Thanks guys. Why is life so difficult?

I had a look at SAE on the web and yes, it looks like it changed to UNF.

I think it would be unlikely to be a cycle thread being as it is on a car. The confusing thing is that some parts seem to be Whitworth / BSF and others are metric (strange for a British pre-war car).

It is from a Lockheed brake system and I think Lockheed are / were an American company so may explain the SAE origin.

A 3/8 W 7/16 BSF spanner fits the head.

I will probably try to dress the damaged heads with a file so that I can get a good fit with a smaller metric spanner or an adjustable. Either that or try to get some NOS or used ones from a classic car spares dealer.

PS. Bonny. The MD metric size table is useful and based on the major diameter it certainly looks like a 7/16 UNF 20 TPI bolt with the head turned down to create the shoulder which engages the banjo union top.

Thanks for the offer of the bolt Beeza. I may take you up on it when I get the cylinders back which are being resleeved in stainless at the moment.

Jim

[chaterlea25]

HI Lawnmowerman,
Correct!! the reason the threads are 20 tpi (UNF) is that they are made under Lockheed patents
Even some Japanese brake caliper pistons from the 80's were made in inch sizes
Regards
John O R