EW350 Fuel tank to frame bolts

[SteveTea]

I need to replace the four bolts that hold the fuel tank to the frame of my 1926 EW350.  Can anyone tell me what threadform was used for these fixings?  Many thanks.

[EW-Ron]

I have looked at my EW and noted that the tank bolts are a motley lot.
Unreliable conclusions may be drawn from this !

The threads seem to approximate best to 6mm, which CANNOT be right.
(which may make them BA something ??)

I'll be curious as to the definitive answer...

[eddie]

7/32" x 24tpi seems to have been Douglas's preferred size for mid 20's tank bolts.

 Regards,
               Eddie.

[EW-Ron]

I see that size mentioned for the TS tank bolts, for quite some years.
That would be a BSW 7/32 size.

Not the best photo, EW Hex tank bolt, I'll try again




Image converted to linked file and shadow detail increased - Dave, 10June2023

[SteveTea]

Thanks for the responses so far.
After playing around with my stock of old bits and bobs I found one screw that sort of fits into the tank and that has a 32 TPI pitch and a measured diameter of 3/16.  However, it did feel a bit loose so the suggestion of 7/32 may well be the correct size, but not the pitch suggested.

So, if I tried to get hold of a 7/32 x 32 TPI screw, would I be correct in assuming a Whitworth thread form?

[EW-Ron]

So, if I tried to get hold of a 7/32 x 32 TPI screw, would I be correct in assuming a Whitworth thread form?

Not really.
7/32 BSW is listed as 24 tpi
And mine - shown above - is that.
(despite a 6mm nut threading onto it quite nicely.)

Your screw with 32 tpi sounds like a 10-32
Is it possible thats its loose enough that only a few threads are catching,
so it feels like it fits ?
( We haven't seen your tank, so anything could have been done to it along the way ! )

P.S. Nice work brightening up my photo there Dave.
My editing prog is on another 'puter - it'd be easier to try for a better pic.

[EW-Ron]

12-24 UNC machine screws would appear to be (approx) the UNC equivalent.
Have to find some to try ?

https://cdn11.bigcommerce.com/s-4c813/images/stencil/1280x1280/products/3259/7794/MPMXS520Ha__55009.1612307349.jpg

The genuine hex Whit/BSW version might be tough to locate ...

Have I got this right.
The more I look at these small sizes, the more convoluted it seems to become !

[Red]

Hi Steve

I have checked the retaining screws on my EW tank and as Eddie has already said they are 7/32 x 24tpi which is a whitworth thread. You can can get hold of hold taps and dies from Tracy Tools but failing that I am happy to let you borrow my 7/32 whitworth tap and die set. My address and details are on page 2 of the Conrod and you will find my telephone number on page 18 under the Surrey/Hants section. You can always give me a ring.

Roy

[SteveTea]

Hi Red,
Many thanks for the offer to use your 7/32 taps, thats very kind.  As you'll see from my next post I have resolved the problem.

[SteveTea]

All,

Many thanks for your information and suggestions, it all helped to point me in the right direction.  In the end I took the tank to a local machineist/engineer who after checking the threads told me that in his opinion the required bolts would be either 7/32 Whitworth or 10-24 UNC, he advised that the UNC would be easier to source.  Both of these threads are 24 tpi so my belief that the threads in the tank were 32tpi was completley wrong!

I have obtained some 12-24 UNC bolts and they fit very well so my problems are over ...... till the next one!

So, although UNC worked for me the Whitworth may well be the "correct" screw as there is very little difference between the two thread forms.