Lister D magneto

Good Afternoon. I'm after some advice please. What thread size are the set screws that fasten the magneto down to its base on a Lister D. The ones currently in place are badly corroded and need replacing.

What make/type of magneto they "may" be different, I can check if I know the type.

Maryalice

Alan,
If its a Lucas RS1 then they are 3/8-16 UNC.

Mike.

Sorry I forgot to say its a RS1, thanks for the size Mike.

May I suggest that the thread would be 3/8 whit, it has the same pitch and dia as 3/8 UNC but its thread angle is 55 deg where as the UNC is 60 deg, Listers used Whitworth on its engines and I would be surprised if the magneto manufacturer would use UNC.
Now I know the magneto I will check the threads.

Maryalice

I've just run a 3/8 WHIT and a 3/8 UNC tap through the base of my spare RS1 mag, the whit screws in freely and after two turns the UNC binds.

Maryalice

Thanks Maryalice for taking the time to check, I picked up some 3/8 Whit for another project so that saves me some time.