Rear frost plug block off plate

[devon lock]

I am installing a Haisley rear frost plug block off plate on my 12 valve, what is the thread size on the back of the block.
For the coolent line do I run it from the frost plug plate to the heater return line.

 

[06 DIESEL]

I believe that you are referring to the freeze plug. If so the bolts are M12X1.75.