1932 Coventry eagle Silent supreme

[ramwing7]

Does anyone know the stud size for the carburetor studs on a 1932 Coventry Eagle Silent Supreme with the proprietary Coventry engine?
 Mine are in pretty nasty shape. 
I've tried to replace with a 1/4" x 26 tpi BSC on one end and 1/4" x 20 tpi on the other and that's a no go.

This thing is going to be a bear to revive.   

[R]

You don't have the old studs to work off  ?
A thread gauge is near indispensable for this.

What happens when you try these sizes ?
They nearly have to be bsw or bsc   in 1/4".

Some marques (in the 1920s) were famous for 'developing' their own sizes.
Douglas for example used some 27 tpi.
But that was more the 1920s.

[ramwing7]

Nope, but I have one ordered. 

[geoff.godwin]

If 1/4in bsc is too slack try 9/32 bsf  .It is still 26tpi and just a 32nd bigger . I have used this size to repair a fair few 1/4 bsf  ,also 26tpi . the tricky bit is getting hold of good 9/32 taps and dies Geoff