Engine freeze plug diameter

I want to install a freeze plug block heater, but I do not know the size of the freeze plug. If you do would you please lmk. The USA & Canada do not show one an accessary freeze plug kit. One parts guy said Stant made one, but I have had no luck there.. I have emailed Germany for their Mazda 2, but that seems like a very unlikely outcome. Thanks to all.

Michael