Classic air tank

Hi all

Anyone know what size/thread the drain plug is in the end of a classics Eas air tank???

On the P38 it's 20mm X 1.5mm. pitch parallel thread, actually measures 19.8mm dia.:5bcheers2:

Just for future refrence its a 1/2" NPT thread.

Makes sense cos when they bought out the P38 they went metric....or the bits that suited them. Example, the bell housing bolts on the 4.6 are 3/8UNC and the rocker cover allen screws are still 1/4UNC yet the plenum bolts are M8. Talk about a box of liquorice allsorts!!!
Wouldn't be surprised if there is a Whitworth or BSF tucked away somewhere. Considering it's a so called British motor you would have thought that the air fittings etc, would have been BSP but that is too logical