Dienut for radiator thread 1 1/2"

[Colin Wilks]

I have invested in some posh new black radiator caps with brass inserts for the 65, with a view to having one for town without the temperature gauge, and one for the country with it in (which I understand was the done thing back in the day). The previous owner had used a chrome cap with a grub screw to secure it and so the threads on the radiator are somewhat knackered. I have been tickling it gingerly with a thread file, but a dienut would do a much better job. 

Does anyone have a 1 1/2" x 16 tpi die nut they would lend me please? I assume it is a Whitform rather than a 60° thread, but am not sure on this.

If anyone can help, please PM me.

Colin